Reorganized and completed menus:

- Separated "File" into "Filters and "Messages" menus.
- Added "Enable filtering".
- Added "Reload messages file".
- Added "Go to first message".
- Added "Go to message".
- Added "Go to last message".
- Added "Display message header"
- Added "Display brace"
- Added menu key shortcuts (mnemonic and accelerator).
Created an entry box for message goto input number and modified the search function to select the closest lower number if input number is not present in messages list.
Cleared message content view when needed.
Blocked message content redisplay when not needed.
Added a signal handler to capture events on message list tree view.
Modified message content display format.
Modified some log points.

git-svn-id: http://svn.eurecom.fr/openair4G/trunk@4426 818b1a75-f10b-46b9-bf7c-635c3b92a50f