Added basic pip install jobs to CI

This merge adds some more CI testing jobs that run

    - python -m pip install .
    - python -c "import bilby"
    - python -c "import bilby.core"
    - python -c "import bilby.gw"
    - python -c "import bilby.hyper"
    - python -c "import cli_bilby"

to test that the basic package configuration is ok (mainly that dependencies are well defined).

This exposes an issue introduced with 0.3.6 that astropy is explicitly required.

changed milestone to %0.4.0

approved this merge request

I've merged master into this branch and just running the ci on my branch https://git.ligo.org/gregory.ashton/bilby/tree/duncanmmacleod/bilby-ci-basic-setup

merged

I checked that it worked on my branch and merged manually (to avoid any weirdness with merge conflicts)