Allow specifying exact pitch values in pitch dicts

[Kuuuube]

The current pitch downstep format disallows certain nonstandard pitches and words/phrases with multiple downsteps.

One obvious but wrong idea to fix this may be to simply allow multiple downsteps. This falls apart when trying to handle both odaka or nakadaka pitches and something non-standard like HLHHL. To cover all bases, dictionary creators must be allowed to specify exactly where they want to high and low pitches.

Test dictionary (search 打ち込む): valid-dictionary1.zip

Example of this pitch format in a dictionary:

"pitches": [
    {"position": "HLHL"}
]

Currently using -1 for the pitch position display and handlebar if there is no downstep. And the pitch category handlebar helper will return null in this case.

[Kuuuube]

This should be good to go now.