FXFormFieldTypeLabel no longer pushes subform when tapped.

This fixes an issue I had when trying to make a Field readonly.

This particular field's `valueClass` conformed to the `FXForm` protocol
which meant that a `UITableViewCellAccessoryDisclosureIndicator` was
shown and, when tapped, a subform representing this field would be
pushed onto the navigation stack.

This fix does two things:

* it abstracts the `isSubform` logic into a readonly property of
  `FXFormField`
* `isSubform` now always returns `NO` if the field's `type` is equal to
  `FXFormFieldTypeLabel`
Only mess with the content inset/offset when the view controller is NOT a table view controller. The UITableViewController already takes care of these behaviors. I was seeing issues when it was trying to duplicate it.
Check class on the delegate, which SHOULD be the view controller
Merge pull request #47 from bartvandendriessche/fix/FXFormFieldTypeLabel_should_make_subform_readonly

FXFormFieldTypeLabel no longer pushes subform when tapped.
Fixed issue with label type fields
Merge branch 'master' of https://github.com/nicklockwood/FXForms

Conflicts:
	FXForms/FXForms.m
Merge pull request #57 from lohilabs/UITableViewControllerFix

UITableViewController scrolling and offset fix
Merge branch 'master' of https://github.com/nicklockwood/FXForms
Updated to version 1.1.3
Deleted spurious files
Merge remote-tracking branch 'upstream/master'