Discover the existing heading preset on document load

[caffodian]

Figure out what the current preset should be, based on the headings already in the document.

Alternately, we could add an extra invisible element that stores the preset, but that seems annoying to everything we've already done.

[caffodian]

However, storing the extra invisible element would allow for presets to more easily change

[caffodian]

idea:

assert all headings of the same level have the same bullet styling class
candidate_presets = copy(all_presets)
for all heading levels:
    for all candidate_presets
          if the candidate preset's bullet doesn't match the current heading level's bullet, remove it from candidates
    if one candidate remains:
         return it

return one of the few remaining candidates (somehow we didn't have enough information to determine which one it should be)

[caffodian]

with the default settings, we should never need to go past the first heading level, since all the first levels differ

[caffodian]

the ultimate worst one would be if all presets only differed on the 5th level

[caffodian]

Ideally this function should be exposed on the plugin, this will make for less bad testing.

[caffodian]

Updating things in place is annoying

[caffodian]

boo @ sketchy set support in IE11 as well

[caffodian]

Something that sucks kinda, is we'll always have 1.1.1.1.1. to fall back on if we can't detect something.

[caffodian]

The default case also sucks because it never gets removed. This is why even on sets where we actually detect correctly, the "return first" idea doesn't wokr

[caffodian]

So after fixing some bad mixups due to my unpolished variable naming, we actually run into the issue I hypothesized above, which is that we shouldn't consider "1.1.1.1.1." as a candidate until all others are exhausted