wt-status: make full label string to be subject to l10n
wt-status: make full label string to be subject to l10n

Earlier in 3651e45c (wt-status: take the alignment burden off
translators, 2013-11-05), we assumed that it is OK to make the
string before the colon in a label string we give as the section
header of various kinds of changes (e.g. "new file:") translatable.

This assumption apparently does not hold for some languages,
e.g. ones that want to have spaces around the colon.

Also introduce a static label_width to avoid having to run
strlen(padding) over and over.

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git