Fix incorrect unsubscribe on Dispose

was subscribed to Click but unsubscribing from LongClick
Fix #638 - Mac Binding build is failing.
Change fields case to _lowerCamelCase to make them (more) consistent with the rest.
Merge pull request #639 from ashokgelal/fix_#638

Fix Mac Binding build is failing
Merge pull request #633 from rb1234/v3.1

Fix incorrect unsubscribe on Dispose
Merge pull request #9 from MvvmCross/v3.1

track update.