Help texts uniformized

Conflicts:
	src/matlab2tikz.m
needsPgfplotsVersion added

 - also added in errorbarMode
formatPgfplotsVersion added
pgfplots version in output and info message
Merge branch 'pgfplotsVersion': fix #306

This puts the `pgfplots` version into the output. The `compat` option
of `pgfplots` is NOT affected in standalone mode: it is always `newest`.