removed unused LLWeb functions for opening non-web media
moved logic inside floaters and away from auxiliary functions

First pass - no Push-To-Talk functionality.

EXP-1299 Nearby Voice floater can't be closed by clicking the sidebar button again.
EXP-1306 Prompt text to "Change your avatar" and "Destinations" floaters get pushed down one line when the floater dialog gets resized to minimum width

moved floater snap region to middle of toolbars and constrained floaters to that snap region
also made toybox floater pass all drag and drop events along to toolbar

reviewed by Leslie

EXP-1300 : drop tool animation. First shot. Works but still a bit hacky and with some bugs (tools can be duplicated at times).

* Fixed setting to always display the inbox inventory panel.

  with.
* LLAgent now keeps track of whether or not the agent can build in the current
  parcel.
* Hooked up is_enabled_function to build and speak commands.

fixed close button not working on floaters against right edge of window
fixed drag and drop only working once per toolbar button
reimplemented drag and drop threshold

 * About land
 * Appearance
 * Gestures
 * Inventory
 * Map
 * Nearby voice
 * Snapshot

removed hover highlighting of buttons when dragging over them
also updated toolbar button art to match spec