Add powerline.tcsh

Ref #762
Add space to rprompt

According to tcsh documentation `%{%}` must not be the last segment.

Note: this means that right prompt has *two* characters between its end and 
terminal emulator border.
Fix tcsh escaping
Add tcsh tests
Strip anything but prompt from tcsh tests

There are some problems with a number of spaces on travis: it differs. Cannot 
use the same code as for fish because output looks like

    {prompt}{spaces}^[0m ^[[{number}D

and both `{spaces}` and `{number}` differ on my machine and in travis.
Merge pull request #773 from ZyX-I/tcsh

Add tcsh support

Fixes #762.