Merging release into master (#376)

* Remove extra line

* Release 0.12.0 (#373)

* Make location of config.json file configurable using environment variables (#350)

* Make location of config.json file configurable using environment variables

* Update minor version to 0.11.3

* Fix column drop issue when first row has missing value (#353)

* Remove extra line

* initial fix of dropping columns

* add unit tests

* revert sql query test change

* revert sql query test change 2

* bump versions

* move outside if

* Adding a working Docker setup for developing sparkmagic (#361)

* Adding a working Docker setup for developing sparkmagic

It includes the Jupyter notebook as well as the Livy+Spark endpoint.
Documentation is in the README

* Pre-configure the ~/.sparkmagic/config.json

Now you can just launch a PySpark wrapper kernel and have it work
out of the box.

* Add R to Livy container

Also added an R section to example_config.json to make it work
out of the box - and I think it's just a good thing to have it
anyway, otherwise how would users ever know it was meant to be
there?

* Add more detail to the README container section

* Add dev_mode build-arg.

Disabled by default. When enabled, builds the container using your local
copy of sparkmagic, so that you can test your development changes inside
the container.

* Adding missing kernels

Was missing Scala and Python2. Confirmed that Python2 and
Python3 are indeed separate environments on the spark
container.

* Kerberos authentication support (#355)

* Enabled kerberos authentication on sparkmagic and updated test cases.

* Enabled hide and show username/password based on auth_type.

* Updated as per comments.

* Updated documentation for kerberos support

* Added test cases to test backward compatibility of auth in handlers

* Update README.md

Change layout and add build status

* Bump version to 0.12.0 (#365)

* Remove extra line

* bump version

* Optional coerce (#367)

* Remove extra line

* added optional configuration to have optional coercion

* fix circular dependency between conf and utils

* add gcc installation for dev build

* fix parsing bug for coerce value

* fix parsing bug for coerce value 2

* Automatically configure wrapper-kernel endpoints in widget (#362)

* Add pre-configured endpoints to endpoint widget automatically

* Fix crash on partially-defined kernel configurations

* Use LANGS_SUPPORTED constant to get list of possible kernel config sections

* Rename is_default attr to implicitly_added

* Adding blank line between imports and class declaration

* Log failure to connect to implicitly-defined endpoints

* Adding comment explaining implicitly_added

* Pass auth parameter through

* Fix hash and auth to include auth parameter (#370)

* Fix hash and auth to include auth parameter

* fix endpoint validation

* remove unecessary commit

* Ability to add custom headers to HTTP calls (#371)

* Abiulity to add custom headers to rest call

* Fix import

* Ad basic conf test

* Fix tests

* Add test

* Fix tests

* Fix indent

* Addres review comments

* Add custom headers to example config

* bumping versions

Author: aggFTW