Community haskell stack binder link

Pin conda version to $CONDA_VERSION

Pin the conda version so that a call to `conda update --all` will not
cause conda to update itself to a higher version with possible breaking
changes.

Motivating example: Upgrade from __4.6.*__ to __4.7.5__ causes the build to fail
due to a conda error:

    [Errno 13] Permission denied: '/.cph_tmpilpdzq7x'

Resolves #891

Add binder link to Community Stack crosscompass/ihaskell-notebook.

Add `Specific Docker Image Options` for jupyter spark

Apply additional tags to base-notebook

* python-<version>
* notebook-<version>
* lab-<version>
* hub-<version>

jupyterhub 1.0

Update to Spark 2.4.3

Update RTD config file to v2

Community Stacks documentation ihaskell-notebook

Add ihaskell-notebook to the list of Community Stacks.

Changed `conda clean` flags to `--all -f -y`

Resolved conflicts between local branch and updates to the upstream
master.

More translation fixes

* msgstr fields should be empty
* File extension should be .po

Do not trigger another docs/local/en update and push
to master when localized text changes

Need to check file changes in TRAVIS_COMMIT_RANGE

Draft pages about translation

Setup travis en template update