Global attribute name standardization for widgets
Better attribute names + other cleanups in widgets
#325

- 1), 2) should be fixed with this update
- 3) should be defined what should happen

Open question:

- I don't know if large and small should be exclusive or.
I guess so, but it was not.

Note:

- I tried to minimize updates to the btnClasses map but that didn't work
I filed a but, see code comment on method `updateBtnClassesJob()`

#786

- I think the button tests is thoroughly.
It can be refined of course if issues occur
or if someone has ideas what can be additionally tested

Note:

- drone.io doesn't install content_shell by default
this has to be done manually (I haven't done it myself yet)
if you add `test/run.sh` to the build script for drone.io the test will probably fail
initial WIP library
nits
add js linting
nits
cleanups
Optimize git checkout.
Merge remote-tracking branch 'upstream/master' into merge-spark-button-changes

Conflicts:
	widgets/lib/spark_button/spark_button.dart
	widgets/lib/spark_button/spark_button.html
	widgets/pubspec.yaml
Upgrade spark-button test to new Polymer and new spark-button
support for running pub on folders
Renamed test sources to disambiguate
Fix spark-button test (noPadding still fails due to a bug in spark-button itself)
Remove unnecessary delays from spark-button test
spark-button test: comments + additional CSS class check
Import, upgrade and fix the WIP spark-button test from @zoechi's pending PR #1430
Emulate a more realistic usage of spark-button in hypothetical code
Fix noPadding attribute not working when set programmatically as opposed to statically

This worked:
  HTML: <spark-button noPadding></>
But this didn't:
  HTML: <spark-button id="btn"></>
  Dart: (querySelector('#btn') as SparkButton).noPadding = true;

The reason was the half-working support for data-binding in an inline <style> tag in a Polymer custom element's markup: when used around an inline <style> tag, <template if="{{noPadding}}"> worked for statically set noPadding, but failed to see programmatic changes to it, as described above.
Merge pull request #1879 from ussuri/fix-noPadding-in-spark-button

Fix spark-button: noPadding attribute didn't work when set programmatically (vs. statically)