Added menu items and calback functions to open and save filters files.
By default, the signal list tree view show the last received signals, this can be stop by selecting manually another signal (not the last one).
Removed the "new" button, the signals list is cleared before each new aquisition or when opening a messages file becausethe signal list may not be compatible between to list of signals!
Enabled column header clicks and created callback functions to display and modify column filters.

git-svn-id: http://svn.eurecom.fr/openair4G/trunk@4316 818b1a75-f10b-46b9-bf7c-635c3b92a50f