Better history widgets

[RealKC]

• Create a custom grid view widget for the history in the main panel
  • Currently the standard gtk widgets just load all the items in the model at once, we should make something that only loads viewable items (I think we'd need to manually implement the scrollable interface for this)
• Add a list view that displays file paths, date when screenshot was taken and url that it was uploaded to. It should be accessible through the history button. It should also have a context menu with the same options as the one in the main view
• Hide the history button when history is disabled (eccaf5d)
• All the above widgets should have context menus for their items that allow you to copy images, urls, etc