Simplify install

[amarkpayne]

Just a couple of quick fixes to make the installation process easier. With these changes, you only need to create the conda environment from the file. The instructions to install the other dependencies such as rdkit and mpmath are no longer necessary

[amarkpayne]

Assuming this last commit passes I have added the last of the remaining commits for this PR and it should be ready for review. I have tweaked the Travis tests so that it now runs two tests:

1. Test using the RMG-Py and RMG-database binaries from the afm channel. If this test fails because of RMG related issues then it means that the binaries on the afm channel need updating.

2. Test using the afm_latest branch of both RMG-Py and RMG-database. This allows you to quickly determine if a quick patch to RMG-Py can resolve a given issue without having to worry about compiling the latest binary. You can even use a temporary commit to change which branch is used for this test by tweaking the .travis.yml file.

The ultimate goal of this is that AFM users get RMG-Py through a conda binary so that they do not have to check out specific branches of RMG-Py and RMG-database, simplifying the installation process (the install instructions are now just clone the repo, make the environment from a single file, and they are good to go).

In practice though it might be best to ship a joint AFM/RMG-Py binary just in case we decide later on to merge AFM back into RMG-Py or submodule AFM in RMG-Py.