Rename btn-new, btn-create and btn-save to btn-success
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Remove slash commands from Markdown preview and display their outcome next to
the text field.
Introduce new "explanation" block to our slash commands DSL.
Introduce optional "parse_params" block to slash commands DSL that allows to
process a parameter before it is passed to "explanation" or "command" blocks.
Pass path for previewing Markdown as "data" attribute instead of setting
a variable on "window".

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

With new navigation design it makes no sense to duplicate title in the
header
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Now it will work on any field inside that form, and it's easier to scope
new behavior, which is what we're adding next!