add .cmd extensions to makefile.win

I was getting the following error while running make all on my windows machine
"""
node_modules/.bin/bower install
'node_modules' is not recognized as an internal or external command,
operable program or batch file.
make: *** [stamp-bower] Error 1
"""

This was resolved by adding the complete extension to the windows path.

Added login-panel placeholder and roster-item Name translations

This will allow to translate 'user@server' and 'password' in the login
screen and also in the roster-item tooltip, there's 'Name:' which can
now be translated

Fixed an error that appears when unload event is triggered

This happens when you load a page with converse and do not login to
the chat. It can be tested in converse.org preserving logs while
navigating to another page.
Inside clearSession there's a call to roster which is not initalized
and also another one to controlbox.save which is not set so it fails
with an url error during sync.

Manual login doesn't work when websocket_url is set and not bosh_service_url

It's already a while since we don't include an input for the bosh_service_url in the login panel.

Put the code that inserts a chat box into the page in it's own method,
so that it can be overridden from a plugin.

to make it clearer what a JID should look like.

Make the text part of an input-group a bit wider and other padding/margin
tweaking.

Conflicts:
	locale/en/LC_MESSAGES/converse.po

Note for debian & ubuntu users

- Added a stamp file for bundler.
- We now specify binary paths for bundler and Sass.
- Added a step "watch" to watch the Sass files.
- Add map file for Sass/CSS

Made some modifications to the code contributed by @thierrytiti and documented
the change.

Fixes #344