remove returned m2t struct where not needed

* add FIXME tag to `addIfNotDefault` since the function is used nowhere
* `cdata2colorindex` is not modified as per discussion in #477
Gitter integration into Travis CI
HipChat integration into Travis CI
Slack integration into Travis CI
Merge branch 'chat-integration-travis' into develop

I've added integration into our Travis-CI scripts to interact with
three different free chat services:

 - http://www.hipchat.com/gxkW23boK
 - https://gitter.im/matlab2tikz/matlab2tikz
 - https://matlab2tikz.slack.com

I would evaluate each of them in terms of features (e.g. mobile apps),
ease of use, availibility of public chat access (?), history retention, ...

Having such a chat room would allow us to communicate outside of GitHub
and not abuse issues for discussions. The chat form is more short-lived,
but that has the advantage that if some people are available at the same time
that we can make decisions in shorter timespans.

Even if we don't use those, such a chat room integrates both with GitHub and
Travis CI. This integration gives an overview of what has happened over time
to the repository and the tests.

Eventually, we should (however) settle for a single service to communicate.
But the best way, IMHO, is to just test-drive them and see what we like.
fix handling of colorbars in R2014b

* E.g., testcase 96 `colorbarLabelTitle` failed due to the colorbar being filtered in R2014b
* The filter was extended to properly handle colorbars in R2014b
* Comments were updated a little bit
remove duplicate check for colorbars
use TikZ default style for 'dash-dot line'

* MATLAB: LineSpec
* PGFplots: Chapter 4.7.2 Line Styles
Merge pull request #490 from PeterPablo/improve_linestyle

use TikZ default style for 'dash-dot line'

Inspected visually.
Merge pull request #488 from PeterPablo/fix_R2014b_colorbar

fix handling of colorbars in R2014b
Axes level caxis scaling
Rescale only if CLimMode 'manual'
Minor comment edit

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
point meta min/max always with colorbars
[Add] missing getEnv and isVerBelow added to test suite
Merge pull request #495 from okomarov/fix_testSurfShader

[Add] missing getEnv and isVerBelow added to test suite
Close opened fid for m2t if errors
Exception compatible with Octave
Exception compatible with Octave (reverted from commit 17cf4dbdbd4acaac4fdbf35eb2bc0c185d4e67a5)
Close opened fid for m2t if errors (reverted from commit 81838fd1bac0f945050ddd976238c7974e23dd58)