add source tag to changeset by default

[leite]

This pull request partially addresses #111, #10 and accomplishes the following:

• Sets autoSourceTag to false by default;
• Add source to changeset by default, see source.

It's known that source property on tags is a bad practice nowadays. because of it I tried to remove autoSourceTag property and source tag button at properties dock.

But I failed because this mess with localizations, how do I remove "dead code" and update localizations?

[Krakonos]

I still haven't found to review it, but I suspect I would prefer this field to be editable in the "Upload" dialog. It can be that user has some imagery active, but is uploading from survey data. I personally do it frequently, as the imagery helps me remember the terrain and topology.

Regarding removing localization: Just remove it. Nothing should go wrong, the texts will become dead too, and will eventually be removed from the localization data. This happens when I sync the data to transifex and pull new translations.

[Krakonos]

Hi! I have reimplemented this changed in PR #281 , including the desired UI changes. Feel free to give it a try and provide feedback.