Change "Created on X" and "Uploaded on X" to "Created: X" etc.

Based on enwiki feedback by Jonesey95: "Created on…" does not work
well when the date is not a day (and we have dates like "1992" or
"circa 1400"). "Created: …" works reasonably well for everything.

Same for "Uploaded on…".

Change-Id: I46b51880be2151a467ccb90a76dde6efc5991cd5
Merge "Change "Created on X" and "Uploaded on X" to "Created: X" etc."