Closes #3182

Used by Android >= 5.0 to make the top bar colored.

Reference: https://developers.google.com/web/updates/2014/11/Support-for-theme-color-in-Chrome-39-for-Android

Most commit in Git are expected to follow standard of single header line,
followed by description paragraphs, separated by empty line from previous block.

Previously Gogs were treating everything as single header. Now we are trying to
render only first line as header, but following lines (description chunks) as a
verbatim.

Signed-off-by: Unknwon <u@gogs.io>

The "PHP" formatting function doesn't add anything, except an undocumented date format.

All usages in the templates have been replaced with DateFmtShort and DateFmtLong for convenience.