separate model variables and obs variables types

[twsearle]

Description

Use the new oops::ObsVariables for observations and oops::Variables for model variables.

Issue(s) addressed

Resolves #90

Impact

Resolves compile-time errors due to recent oops changes, alongside an out-of-bounds error in the Increments class.

Checklist

• I have updated the unit tests to cover the change
• I have linted my code using cpplint
• I have run the unit tests
• I have run mo-bundle to check integration with the rest of JEDI and run the unit tests under all environments

[twsearle]

I am seeing a lot of mo-bundle issues that don't seem to be related to my change, but might be related to me commenting out all lfric etc libraries:
http://fcm1/cylc-review/view/tsearle?&suite=mobb-oops2591&no_fuzzy_time=0&path=log/job/1/cmake_mo__cray_gnu_debug/01/job.err

changes look straight-forward to me otherwise and unit tests pass. If I get a green light I will push ahead as we really want to fix this up as quickly as possible to be able to run all the comparison tests etc.

[mo-joshuacolclough]

Thanks @twsearle this looks good by-eye. The build can't be any more broken than it is already!

Conversely, I've run a test with only the lfric-related repositories and it passed so you should be good to include those. The only problematic repo may be opsinputs and ops-um-jedi since that might be using opsinputs?