Add button for linking internal page

[maxxer]

It would be great to have another link button in the toolbar to link an internal page. An user should be asked for page title or alias, and the resulting url should be automatically generated.

[bupy7]

@maxxer Need to create a new plugin for Imperavi editor. If you can do this I will wait your pull-request. =)

[maxxer]

I see 😆 unfortunately I don't have much time now, I'll leave open in case someone else does (or I will)