Add user control to display up to two help images.
Help images: improve resource image file naming and prepare for different images in Pull, Merge and Rebase dialog
Enable autosize for HelpImageDisplayUserControl
FormPull: use HelpImageUserControl instead of PictureBox
FormRebase: use HelpImageUserControl instead of PictureBox
FormMerge: use HelpImageUserControl instead of PictureBox
HelpImageUserControl: white background and autosize
FormPull: Use new help images
no autosize
FormMergeBrance: use new help image
FormRebase: use new help image
FormMergeBranch: sizing fixes
FormPull: show fast forward help image version on hover
FormMergeBranches: show fast forward scenario help image on hover
Help images: fix distances for hover
FormPull: add merge and rebase icon
Don't set previous messege when amend is unchecked
SettingsDialog: Implement Goto Plugins section
Plugins --> Settings: open new settings dialog (with Plugins section preselected). Remove old Plugin settings dialog code.
SettingsTreeViewUserControl: fix event handling