MSGIDs added to warnings and errors

MSGIDs allow for better error checking.
Also used the built-in sprintf functionality of error/warning
where string concatenation was used.
Replaced errors starting with "Function XXX" with a proper
MSGID of the form  "matlab2tikz:XXX:msg"
translateMarker simplified

big switch-case with nested ifs replaced by switch-case followed by if
Automatically import plotmarks in standalone mode

plotmarks is required for some marker styles, but it wasn't imported
in the standalone template, thus causing possible bugs
Merge pull request #238 from egeerardyn/msgid

MSGIDs added to warnings and errors
Merge pull request #240 from egeerardyn/translateMarker

Translate marker
removed unused function append()