Configure ESLint, fix ESLint errors

[rhansen]

Multiple commits that set up ESLint and fix the issues it complains about:

• Configure ESLint
• Run eslint --fix .
• Fix comments
• Combine two string literals into one
• Delete unnecessary else
• Fix comment indentation
• Switch single and double quotes in HTML string
• Use this instead of self where possible
• Enable strict mode everywhere
• Delete unused imports
• Delete most unused variables
• Delete redundant variable redeclarations
• Delete commented-out code
• Delete dead code
• Use const and let instead of var
• Rename ep_comments class to EpComments
• Simplify handling of "Show Comments" toggle
• Use camel case for variable names
• Remove redundant ESLint global declarations
• Reduce global namespace pollution
• Use jQuery to build HTML
• Fix various minor ESLint errors:
• Don't iterate over inherited properties
• Simplify comment counting
• Rewrite getSelectedText for readability, robustness
• Delete redundant jQuery imports
• Avoid mutating passed-in list
• Capitalize PreCommentMarker class name
• Add missing variable declaration
• tests: Fix exception error message (copy+paste bug)
• tests: Delete unnecessary wrapper objects
• tests: Switch some function expressions to arrow functions

[JohnMcLear]

So a few things as we discussed..

1) awesome work! 2) I'd really like in the future to see fixes land separate from test modifications, just so we can see that the fixes/patches land and that the software functions as it was before. 3) I'm not strict about function(){} vs () => and for me that's fine.

TODO: Tests are failing :) Will need fixing up before merging!

[rhansen]

TODO: Tests are failing

Yup, though they are failing the same way on master.

[JohnMcLear]

Nice, afaik @ilmartyrk is working on the failing tests.