Add dock with project history

[alexbruy]

Add a dock widget with project history. History is loaded from the server in the background thread when dock opens for the first time, then on each sync history is updated with the new information. Local project version is shown in bold.

Versions in the dock have a context menu with two actions:

• viewing version metadata (author, project size, creation date, user agent, etc) and details (changed tables, number of added/removed/modified records).
• viewing version changes in the diff viewer dialog. Plugin downloads all necessary changesets in the background thread and then uses them to create a diff. Downloaded files are cached and local files will be used when diff is requested again.