Fix crash when auto-updating translations with some TMs.

Fixes #405.
Correct Slovak translation.
Japanese Translation update.
Update Arabic translation.
Add Nepali translation.
Update Hebrew translation.

Some typos fixed.
Updated Lithuanian translation
Fixes to Kirghiz translation.
Return focus Find window's text field when raising.

Unlike when showing for the first time, focus wasn't reset in this case.
Update wxWidgets snapshot.

This should fix focus problems in Preferences.

Fixes #497 (hopefully).
Fix badly formatted ne.po.
Update Spanish translation.
Update Croatian translation.
Add Corsican translation.
Update Kazakh translation.
Fix bad Slovak translation.

Do s/prípad/problém/g -- translating "issue" as "prípad" is completely
wrong (the word means "case") and renders the error message
incomprehensible.
Fixes to Italian translation.
Don't add large dirs to the default TM import set.

Don't add $HOME (or even C:\ on Windows!) to the list of directories to
search when creating a new translation memory.  Scanning the directories
is slow and due to bad UI design, Poedit seems unresponsive.

This is not worth fixing properly, because all this TM import will be
reworked completely.

See #510.
Update copyright years.
Implement find shortcuts.

Use the standard Ctrl+(Shift)+G.  On Windows, also use F3 and Shift+F3
for compatibility with some software.

Fixes #283.