Merge pull request #439 from jjofre/master

Made color of x and y axis in the ErgPlot Window configurable
Fix delete intervals

If multiple intervals are selected then the delete interval
menu item should delete all the ones that are highlighted.

Fixes #442
Remove BlankState menu
UI Nits: default chart fonts smaller

.. the chart labels need to be smaller especially
on small screens, and better to err on the side of
caution and make them smaller.
Let user close blank state

The user can close the blank state screen and
can also click a checkbox to ensure it is not
shown again for this athlete.