Fix invalid XRC markup.

The <usenotebooksizer> property doesn't exist (anymore?).
Require wxWidgets 3.0.
Switch to using Visual Studio 2013 for Windows build.

Main reason is better C++11 support.
Use C++11 initializer for accelerators entry.

It makes adding entries easier.
Fix Ctrl+arrows/Enter accelerators.

Don't use only the numpad, support regular keys as well.

Fixes #548.
Use CRLF for Visual Studio projects.

No real changes otherwise.
Show catalog properties as window-modal.

Modal is not appropriate on OS X, window-modal is better.
Move helper scripts to scripts/ directory.
Add plural forms database.

Make setting up catalogs simpler, but adding database of plural forms
that will be used in the UI and for default values.
Move PO header fixups into dedicated function.
Auto-fill Plural-Forms header if we can.

When loading a catalog with Plural-Forms but without the header,
auto-fill it if known.  Ditto when creating a new catalog from scratch.
Fix dummy headers pre-filled by gettext too.
Move language & plural forms to the top of properties dialog.

The more important fields should be near the top and the language is
arguably *the* most important value in this dialog.

Also move plural forms right under the language field, because they are
related.
Better Plural Forms properties UI.

Offer the choice to use default expressions for a language, if known.

Plural-Forms header is a common source of confusion and errors, doing
this should reduce related problems significantly.
Ignore Visual Studio's *.sdf files.
Add placeholder strings to properties dialog's text fields.
Improve labels for plural forms.

Instead of saying e.g.  "Form 0 (e.g.  1)", use natural labels for the
common forms ("Zero", "One" etc.) and several examples for unrecognized
forms.
Remove unused Ant properties from deps/.

Nothing using VC++ is built with Ant anymore, so no need for these.
Improve readability of some of the default plural expressions.

Most of them use brackets, so use them for _all_, for better readability.
Check for unusual plural forms and warn about them.

It's better to use consistent expressions, so warn about anything
weirdly formatted.  Filter out some common differences (whitespace,
encompassing brackets).