STORM-34 ADDITIONAL_FIX Made saving favorites in file per-account preference instead of per-machine.

- Made changes in code of floater preferences and panel login that were required because of turning the setting per-account.

- Added new method to LLFloaterPreference that looks for current user's record in saved favorites file and removes it.

STORM-34 ADDITIONAL_FIX Implemented storing of multi-user favorites and showing them on login screen.

- Changed the way SLURLs are cached a little, because previous one introduced problems with theit order.

- Also allowed saving of favorites to disk even if not all of them received SLURL info - this is done to avoid favorites not saving when there is at least one "dead" landmark among them.

- "Username" field on login screen is now not a lineeditor, but combobox (to enable autocompletion), but without button (Esbee asked for this in ticket for security reasons, and perhaps for visual consistency).

- Elements of this combobox are names of users whose favorites we have saved in file.

- Contents of "Start at:" combobox are changed depending on changes in "Username"- if username is present in favorites file, favorites for this user are added there.

- New callback was added to LLCombobox and used in this fix, because present ones weren't enough to easily track changes in text entry.

STORM-34 FIXED Saving of user's favorites into file and showing them in "Start at" combobox on login screen was implemented.


Implementation details:

- File is saved on exit from viewer and not immediately on changes as was written in spec. It is done to make this file consistent with favorites order: order of favorites is saved on exit,
so if favorites info is saved in other moment earlier, crashing viewer or other unexpected way of finishing its work (i.e. via Windows task bar) would cause inconsistence between favorites order
saved per account and one from this new file.

- File is saved in user_settings\stored_favorites.xml.

- If you uncheck the option in Preferences and press OK, the file gets immediately deleted (according to spec).


Issues that require further changes:

- Currently only favorites of last logged in user are shown in login screen. Showing favorites of multiple users will be implemented later when design for it is approved by Esbee.

- Preference is now global for all users, because design states it may be changed before login, and we don't have account info at the moment. But it doesn't seem to be a good idea, so changes in design are needed.

- Currently the way of retrieving SLURLs needs optimization in a separate ticket.

More detailed design approved by Esbee is needed to develop it further, perhaps in new tickets.

Besides, removed redundant space before colon.

CHOP-238 Fix to bug introduced by http://hg.secondlife.com/viewer-beta/changeset/4072bd5389b2 Reviewed by Brad

STORM-687 FIXED Applied floater transparency to snapshot preview texture (unless the floater is focused, see STORM-676 to know why).

STORM-677 ADDITIONAL_FIX Force textures inside texture picker to be 100% opaque while the control is in a focused floater.

Besides, made LLFloater handle opacity more like other controls do.

DN-217 Changing between View Display Names on and off during a conference call session put viewer in a state where last name resident was shown in viewer everywhere for user in conference call with last name resident.

Bubble chat color picker now sets the background color for the name tag and bubble chat. Label for the color picker changed to "Bubble chat background"
Removed unused "BackgroundChatColor" setting, using "NameTagBackground" instead.

Added additional check to prevent infinite loop.
Blind fix since we have no repro.

- Deleted unnecessary draw() method that didn't call base LLFloater::draw() method.

- Deleted custom images of floater to use default