Update JSMessagesViewController.m

Prevent frame resize on keyboard WillSnapBackToPoint when the MessageViewController is embedded within a TabBarController
Account for visible keyboard when setting table view insets (closes #126)
Removing the method `viewWillLayoutSubviews` entirely (closes #126)
Merge pull request #127 from kleo/issue_126_adjustedTableViewInsets

Account for visible keyboard when setting table view insets (closes #126)
Merge pull request #124 from mombrea/patch-1

Update JSMessagesViewController.m
simplify tabbar check