MAINT-7099 FIXED 'IM' and 'Voice call' menu items should be disabled for the group, which you have already left

consolidated most indra-specific constants in llcommon under indra_constants.h
fixed issues with operations on mixed unit types (implicit and explicit)
made LL_INFOS() style macros variadic in order to subsume other logging methods
such as ll_infos
added optional tag output to error recorders

STORM-1838 Added teleport request to conversation log.  Added xml to have message appear in IM window, if open.  Code cleanup.

Added "Zoom In" context menu item to Nearby Chat list in People floater and Conversation floater

Added messages, for now they're displayed in two cases:
1) no log entries, logging disabled
2) no log entries, logging enabled
Case when there are existing log entries and
logging is disabled is still under discussion

Set UnreadIMs icon to visible if messages were sent while offline.

CHUI-326 FIXED (One entry per conversation with a user in conversation log timestamped with most recent utterance/activity.)

- Modified LLConversationLog to show only one entry per conversation with user. I.e. there can't be two conversations with the same session_id in LLConversationLog.
- Got rid of processing voice sessions
- Refactored creation of conversation in LLConversationLog
- Refactored a little bit LLConversation and LLConversationLog: function names and made some functions private

CHUI-298 FIXED (Conversation started as an IM and then goes to voice call does not show as call in conversation log)

- Show voice icon when call is started
- Added flag LLConversation::mIsConversationPast which means that this conversation is finished and any of its data can't be changed. I.e. it cannot be reused.
- When session removed (i.e. finished) corresponding conversation is marked as Past conversation. I.e. mIsConversationPast is true.
- Added changed(const LLUUID& session_id, U32 mask) method to LLConversationLog to notify particular conversation. This is used in LLConversationLogList to update its particular item and not to rebuild the whole list.

- Added View Nearby chat history option
- Also replaced menu item "Add Friend / Remove" with two separate menus: Add Friend and Remove Friend. So if user is a Friend the Remove Friend option would be shown there. If the user is not a friend, the Add Friend option would be shown.

CHUI-306 FIXED (Selecting IM option for Group in conversation log does not start an IM if you did not initiate the conversation)

- To start group call or group chat, group_id should be passed as an argument to LLGrupActions, not participant_id.

A brief explanation of what have been implemented. More information can be found in comments.

1. Created conversation history viewer (llfloaterconversationpreview)
2. Created LLConversation and LLConversationLog classes which represent and hold data of conversations (llconversationlog)
3. Created LLConversationLogList and LLConversationLogListItem which are the visual representation of LLConversationLog and LLConversation respectively
4. Created LLFloaterConversationLog - which holds and displays LLConversationLogList