Support experimental branches in update-stable.

Currently only "destruction", though more can be added by changing a
regexp.  It is assumed that anything that doesn't start with a version
number is experimental, not stable.  The game directory will be created
on install, but not the inprogress directory.
Add a launcher for the destruction branch.
Support destruction branch in rebuild trigger.
Fix a typo in config.py for destruction branch.
Use https:// for save backup URLs.
Add experimental dwants branch, move experimental to a submenu.
Another experimental branch, 'jump'
Add 0.13.
Make 0.13 the default.
Remove destruction and jump experimental branches.
Don't mark 0.13 as beta
Allow downloading cores in the save downloader.
Remove destruction and jump from rebuild CGI too.
Update webtiles config for CSZO IP migration.
Remove dwants branch too.
Use crawl-stable-launcher in webtiles