Accelerator for the "Filters" button conflicts with one for the "File" menu

[eumagga0x2a]

A small keyboard navigation and usability issue in the "en" locale:

If not both "Filters" buttons for Video Output and for Audio Output are disabled, the current accelerator Alt+F for these buttons takes precedence and one has to press Alt+F at least twice to access the File menu which I find to be very irritating. I think, it is better to remove the conflicting accelerator. Video filters can be accessed via Ctrl+Alt+F shortcut anyway.

Furthermore, the attached patch adds back accelerators for "Project Script" and "Connect to avsproxy" entries of the File menu which lost theirs during recent rearragements of translation contexts.

(There is a bigger issue that while it is possible to tab through Avidemux GUI elements, none are accessible via keyboard unless they have their own accelerators.)

[eumagga0x2a]

Just for the record: committed as [i18n] Remove conflicting shortcut (euma), thanks!