gui comp: fix autocompletion of dyes too enthusiastic

changes had made the autocompletion fill the name of the closest dye as soon
as a letter was typed. This doesn't work well as it prevents from free typing, and
also cause the wavelength to change immediately. So revert the change.
gui menu: change shortcut from ESC -> Pause

Esc is hard to map, and anyway other control expect to be able to use it.
(For instance SuggestTextCtrl). So instead map it to Pause.

Also display a visual feedback when this happens so that the user knows he did
press the key.
gui streams: improvements when adding a new stream

don't automatically play it, only if a stream is already active.

If it's a fluo stream, also automatically focus on the name to directly allow
the user to select the dye.