Loads more UTs, plus bugfix and notes.

UTs to cover all AS flows.

Bugfix for MMTEL call services in cases where there is no body on the
INVITE - we don't want to crash!

MMTEL flows don't all work yet; failing tests are disabled and
comments inserted in code where we need to make a fix.
Merge branch 'dev' of github.com:Metaswitch/sprout into isc-ut-beefup
Merge pull request #23 from Metaswitch/isc-ut-beefup

[Reviewer: Mike] ISC UT beefup

Code changes look fine.  I haven't reviewed all the UT test cases - I think that would be redundant in our processes.