Appveyor: use newer conda packages and only run all tests on one platform

[janschulz]

Since setting the miktex version as a workaround for the miktex related build failures, the miktex package was updated and an inkscape package was added in conda-forge.

Also install these packages only on one build so that the rest of the builds are shorter...

Also includes the enablement of the conda packages again.

Closes: #6682

[janschulz]

So, this passes on appveyor and now runs the latex (and other) tests in the Py27/32bit build. This is the first build and takes 30min vs the rest which take 7-8 mins. I'm wondering if putting the full tests in the second run would make more sense so that the first run is fast and one can iterate based on the results of that run (assuming that in most cases changes will only touch non-latex codapaths).

Comments?

[tacaswell]

Most of the time when I am waiting on appveyor it is due to there being many jobs stacked up, but re-ordering them to put a fast one first sounds like a good idea.

[janschulz]

And it works... Please have a look and merge if satisfied...