(bug 56412) Make all sidebar phrases on Planet translatable

This patch adds translations for all phrases visible in the
left (right in RTL languages) sidebar at all xx.planet.wm.org
sites.

These are, in addition to the ones already existing, as follows:
"All times in UTC.", "Powered by", "Wikimedia" and "Planetarium".

The translations have been kindly provided by various Wikimedia
community members who shall remain unnamed due to gaps in my
memory :-)

I'm also using this opportunity to add a missing link to the
French Planet Wikimedia as well as to clean up the use of
punctuation inside <h2 /> tags (ie. I'm removing trailing
colons for L10n purposes.

Bug: 56412

PS 5: (dzahn) - tabs to spaces in planet.pp

Change-Id: I189ff52963dcc2cfe821b68f1e16749906240c5a
Merge "(bug 56412) Make all sidebar phrases on Planet translatable" into production