Add timestamp to web update signature; still needs verification
Merge remote-tracking branch 'origin/develop' into web_updates

Conflicts:
	MainWindow.cpp
Further refinements to web updates; should be ready to merge.

Some refinements to the startup, to make a better UX. Also, updates are
checked to make sure their timestamp is reasonable (must be later than
previous update, and must be later than blockchain commit date).
Move web updates repository URL to a header
Merge pull request #38 from BitShares/web_updates

Web updates