Populate the capture bar only when opening Capture mode.

Buggy systems tend to crash when listing the available codecs for the capture bar. With this commit buggy systems will still be buggy but MPC-HC won't crash unless the user really starts capture mode.

This commit fixes #3523 #3533 #3551.
Prepare for a new British English translation.
Add British English translation (ticket #3548).
Fix: Ensure that the "On Top" status is checked when losing the focus.

It used to be checked on being given the focus which is mostly useless.

This commit helps for ticket #3541 but in theory it should just be a safety belt.
Use the proper size prefix in format functions.