fix eslint + stylelint errors

Running "eslint:target" (eslint) task

/Users/thomasc/repos/mediaelement-plugins/src/picture-in-picture/picture-in-picture.js
  20:2   error  Mixed spaces and tabs              no-mixed-spaces-and-tabs
  34:54  error  'media' is defined but never used  no-unused-vars
  48:2   error  Mixed spaces and tabs              no-mixed-spaces-and-tabs
  55:14  error  'error' is defined but never used  no-unused-vars
  61:14  error  'error' is defined but never used  no-unused-vars
  68:2   error  Mixed spaces and tabs              no-mixed-spaces-and-tabs
  71:47  error  'event' is defined but never used  no-unused-vars

/Users/thomasc/repos/mediaelement-plugins/src/playlist/playlist.js
  351:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs

/Users/thomasc/repos/mediaelement-plugins/src/quality/quality.js
   99:9   error  Redundant double negation                            no-extra-boolean-cast
  110:16  error  Redundant double negation                            no-extra-boolean-cast
  398:37  error  'currentQuality' is assigned a value but never used  no-unused-vars

/Users/thomasc/repos/mediaelement-plugins/src/snapshot/Gruntfile.js
  35:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs
  36:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs
  37:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs
  38:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs
  56:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs
  57:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs
  58:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs
  59:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs
  61:2  error  Mixed spaces and tabs  no-mixed-spaces-and-tabs

/Users/thomasc/repos/mediaelement-plugins/src/snapshot/snapshot.js
   11:475  error  'exports' is defined but never used  no-unused-vars
   54:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  108:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  138:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  145:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  147:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  148:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  150:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  151:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  152:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  153:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  154:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs
  156:2    error  Mixed spaces and tabs                no-mixed-spaces-and-tabs

✖ 33 problems (33 errors, 0 warnings)

Running "stylelint:all" (stylelint) task

src/picture-in-picture/picture-in-picture.css
 2:3  ✖  Expected indentation of 4 spaces   indentation
 3:3  ✖  Expected indentation of 4 spaces   indentation
 4:3  ✖  Expected indentation of 4 spaces   indentation
 5:3  ✖  Expected indentation of 4 spaces   indentation
 6:3  ✖  Expected indentation of 4 spaces   indentation
 7:3  ✖  Expected indentation of 4 spaces   indentation
 8:3  ✖  Expected indentation of 4 spaces   indentation
 9:3  ✖  Expected indentation of 4 spaces   indentation

✖ 8 problems

mediaelement / mediaelement-plugins

fix eslint + stylelint errors #192