merged getEnvironment with findEnvironmentVersion

always calling 'ver' with an argument

In MATLAB, the call to `ver` has quite some overhead.
In the ACID test, this amounts to almost 11 seconds, while
writing out the TikZ files takes 13 seconds.

By calling ver with argument, the number of calls to ver
is decimated (no more iterating over calls).
Furthermore, by merging getEnvironment with findEnvironmentVersion,
the number of calls is halved (this amounts to a nearly insignificant gain
compared to the other measure).
However, both functions perform almost the same operation and rely upon exactly
the same intermediate data such that they can/should be merged.
if strcmp(env) -> switch-case-otherwise

strcmpi and strcmp on the environment replaced with switch-cases
to improve readability and robustness.

If another environment should be added, one can search for
the errorUnknownEnvironment and finds all locations where something
env-dependent is going on.
checkDeprecatedEnvironment function added

Removed the functionality from the main method to a specific function.
The minimal accepted versions are still in the main method for clarity.
envVersion stored in m2t struct

This allows to check deprecation at every point, and,
it allows to put the version in the output
Environment in TikZ output

Also show which version of MATLAB/Octave ran matlab2tikz
in the TikZ output. This makes it possible to track environment-related
bugs better.
hggroup, specgraph.contourgroup moved

Moved both to a more logical place: together with the other
cases that call `handleAllChildren`
Default handling: use back-tracking

When an unknown handle graphics element is encountered,
execute the default handling using back-tracking.
Whenever an error occurs, roll back the state of `m2t` to before
encountering the hg-object and continue with the next element.

The original error message is shown for debugging purposes, but
this allows one to run `matlab2tikz` on figures that have
unsupported elements, as was the case in Issue273
Text objects also include background color
environment-related function moved to end

All environment/version related functions moved towards
the end of the file and grouped together
Matlab does not render text fields with a NaN in position-vector. matlab2tikz does now the same (priorly it produced uncompilable tex code where pgfplot got NaNs where it could not handle it).
Merge pull request #275 from egeerardyn/fixIssue273

Fix issue273
Merge pull request #279 from Aikhjarto/master

matlab2tikz produced uncompilable code if NaN was used in a text field as position
Merge pull request #277 from egeerardyn/fixIssue259

Text objects also include background color
Merge pull request #269 from egeerardyn/cleanup-matlab-env

Cleanup MATLAB/Octave environment checks