Disable submit button if form has not any change

[yuiseki]

Split from: #4

We should only be able to be sent when data changes are made.

[LaoshuBaby]

Sorry, this issue should be reopen, its more serious

Because I've succeed in uploading a zero modify changeset by fake input

I fill the source, then input something in any field, then delete it. But the program still think is uploadable.

You can see this reproduce video:

2022-03-21.16-39-35.mp4

Changeset: https://www.openstreetmap.org/changeset/118724702

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To avoid this kind of problem, you'd better diff the data before upload, not only disable the button.