IDEA-130522 PushDialog: Checked repo state should be delegated to model, modify allow  push logic

* current ui check state delegated to appropriate model;
* selection state wrapped into check model class;
* enable push button iff all repository infos are loaded and selection is not empty
(cherry picked from commit cfcbe0d)
push dialog: tree edit target panel cursor changed to HAND_CURSOR

(cherry picked from commit f76e68c)
[push] IDEA-131438 IDEA-130650 Make remote selector independent from edit mode, and notify model about remote change

Introduce a special tag which will be called on click with a mouse
event which produced that click. Use this event coordinates to show
the remote selection popup near the click area.

Add a callback to the PushTargetPanels which should be called when
the target panel changes the model not via the usual edit mode.
(cherry picked from commit 115012f)
[push] Don't render remote as editable if there is only one remote

(cherry picked from commit 66738b8)