Reorganize Preferences tabs a bit.

Move updates-related bits to a separate tab.  Merge General and Editor
tabs together.  The combined General tab is huge now, but will be
updated to look better.
Implement native preferences on OS X.

Use the wxPreferencesEditor class for native behavior on different platforms.
Add ExplanationLabel.

Use dedicated control for auto-resizing explanatory labels that describe
non-obvious settings in some detail.
Use ExplanationLabel for TM's explanation.
Add explanation of the beta updates.
Use gray for explanations in XRC files too.
Add LearnMoreLink control and use it everywhere.

Use unified look for the "learn more" links.  Use a helper class that
hides platform differences.
Convert Extractors pref page from XRC to C++.
Add Extractors explanation to Preferences.

Briefly explain what they are for and what they do.
Reorganize the General preferences page.

Reorganize the page to be easier to navigate and look better.  Group
controls with bold labels instead of outdated static boxes.  Add nicely
formatted explanations.  Rephrase some settings a bit.

Rewrite in C++ instead of using XRC.
Use slightly darker gray for ExplanationLabel.

Improves readability a bit.
Make explanations' indentation consistent.

Use the same indentation everywhere. Align with checkboxes' text.
Move team settings to the bottom of Properties.

They are not as important as the charset, so move them to the very bottom.
Merge branch 'native-preferences'