Merge pull request #1051 from colmjude/master

Add basic space reset functionality
Be more explicit in reset message

We need the user to know that yes, we're going to remove content.

Without it they might think reset means something akin to rebooting
windows: something you do when things seems not quite right.
correctly call the callback in space reset

The previous code would only work when the number of private
tiddlers was one (1).

We want to compare the current index with the number of tiddlers,
and when we've reached the end, then do the callback.

This, however, is still not fully correct. All we are saying is
"the last DELETE has come back with success, so callback". It is
entirely possibly that some other, earlier, tiddler's DELETE is
still pending.

So really we probably want some kind of counter, but this is
at least better.

defering to @pads and @colmjude for final consideration
release 1.2.6

* add space reset button to /_space
release 1.2.7

* make sure remote dependencies are actually there
Hide reset space button if user not member of space

Refers to #1054