Fix mutual exclusivity of --delete and --submit review command options

As per documentation, --delete --submit were supposed to be mutually
exclusive but they were not. Add check to make sure those two options
are not used at the same time.

Change-Id: Ic63573b1e0a455fa879c88bddbdd4fcd05d7d595
Fix broken links to CommentRange entity in changes REST documentation

Change-Id: I35f6ad50d8dbe73df93297b76f4511e484dc9c7e
Update review command documentation for mutually exclusive options

Review command documentation was not accurate regarding the mutually
exclusive options.

Change-Id: Ic5e7fa36a844258a448f37d42f041d350a0d6441
Add example of range comment in REST API documentation

Bug: Issue 2861
Change-Id: Id9db8fd7a56178f469b1ed17d1cac14c78bfff79
Replace "line" with "end_line" when range is given in inline comment

When a range comment is given in the review, the caller must specify
the "range" entity with "start_line" and "end_line" values, and also
the "line" value.

The documentation simply says that the "line" value 'should equal the
end line of the range', but the implementation does not validate this.

If "line" is not specified, the comment is added as a file comment
regardless of what "start_line" and "end_line" values are given in
the range. This can be confusing for users.

Change it so that when a "range" is given, the "line" value is not
necessary, and if given at all will be overridden with the value from
the "range"

Bug: Issue 2861
Change-Id: I5d0d31c392937b1955572781375fc48982ea7664
Gracefully skip mergeability checking on broken changes

If a change is missing its current patch set the mergeablity check
will NPE. Skip the check and just return false, indicating there
was no update made to the change.

Change-Id: Ic82b2db1d2f7d27105a06c4082b51e7308f02b04
Clarify the failing change in MergeabilityChecker

If an update check fails, it may be change specific. Record the
change as part of the logged message.

Change-Id: I33aba050572f919e150d8e0f1bd678f575301b72
Merge topic 'comment-range' into stable-2.9

* changes:
  Replace "line" with "end_line" when range is given in inline comment
  Add example of range comment in REST API documentation