(External tilesets already have this check)

Fix null error in CLI interface.

* Errors not being cleared between maps loads.
* Support for source on external tilesets
* Fix divide by 0 errors on Column = 0 with external tilesets
* Initial messaging to show no support for image collection maps
* Also paving the way for image collection support.
* Remove 0:1 based map choice in the UI only. Code not removed yet.
* Changed NONE tiles to EMPTY
* Support image node in external tilesets

Export new properties

See merge request !2

Usages cleaned up.

(default is the map width)
Fixed old email addresses and links

Add CLI

See merge request !1

Include .zip file for download.

* Replaced parsing with XML de-serialising.
* Live conversion and updating
* File watching for changes from Tiled.