Update README.md
IMproved visual drag&drop and normalkized styles in kanban and taskboard
Add tgHistory directive.

This is a complete rewrite of the old tgChange directive
that has a lot of functions that works only with dom mutability
and with unclear name. This new version works in majority of
time with immutable operations and only mutates the dom in
the last render step.
Remove old tgChange directive code.
Remove now unused history loading code and event handlers.

From issue, task and userstory details modules.
Remove loadHistory call from attachments event handlers.

And replace it with scope event raising. This change is needed
for conserve the previous behavior of history reloading on any
attachment change. The history reloading is now handled by
history directive and controler and them responds well to
'history:reload' signal.

Moreover, loadHistory repeated function is removed from
us/task/issue detail controllers.
Replace old history related template with tgHistory directive

Removing a lot of verbose and repeated html blocks that can be
easy build by tgHistory directive.
Remove unused resource methods for load history.