re-interpret single move commandlines directly

instead of creating a MoveCommand instance.
These will still be created for 'move's that are part of longer command chains
introduce new themable thread.body_focus for focussed body text lines
make focus visible in bodytext parts
added thread.body_focus themable to contrib themes
only insert bodytree if bodytxt is nonempty
Merge branch '0.3.4-fix-faster-move-538' into 0.3.4-feature-urwidtrees

Conflicts:
	alot/ui.py
immediate move commands

this directly passes on move up/down/etc
commands and omits creating a MoveCommand object for speed's sake
make thread.move parent message-based
implement Threadbuffer.focus_foo methods

to move the focus depending on the outmost tree of messages
(not the inner nested threes..)
move focus to summary when collapsing MessageTree
allow collapse/expand on thread.select

when body text lines are focussed
completion for move command
fix typo
fix: thread.select on source text
pep8