"Recent files" now works with non-ASCII paths.

This involved used UTF8 to write file paths in the configuration. The
same thing might be needed for all string variables, now that I think
about it.
Also setting UTF8 as the charset in the startpage.
Read and write string CVARs as UTF8.
Max recent files is now a CVAR.
Early draft of path rendering.

Full of ugliness and sin. Very hardcoded. So hacky. Much work to do.
Merge branch 'master' of https://github.com/sirjuddington/SLADE
Made code compile again.
GFX entry panel fixes

Converting to paletted PNG from the GFX entry panel removed transparency
because when writing PNG it relied on the status of the tRNS menu item
rather than the content of the image, and converting from the GFX panel
did not update the PNG-related menu items.
Optimizing PNG from the GFX panel marked it as modified, prompting for a
save, which caused rewriting the entry and destroying any optimization
done by external tools.
Path rendering work, continued.

Less hardcodedness.
Merge branch 'master' of https://github.com/sirjuddington/SLADE
Path rendering work, continued.

Highlighted interpolation points are no longer rendered as being tagged
by themselves.
Dragon pathing finished!
Factorized "tagged" lookup.
Fix some configs.
Merge pull request #67 from Gaerzi/master

Sync with my fork.
Update CmakeLists.txt for wx 3.0 and webview
Fix for linux compilation
Implemented texture/flat usage count tracking
- Added option to sort by usage count to map texture browser
- Last selected map texture sorting type will be remembered between sessions
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
Entry autosave works again