Add wordcount and lettercount to InfoPanel

[asmsuechan]

context

I want word count and letter count in InfoPanel.

before

Neither word count nor letter count in both a Markdown note and a Snippet note.

after

In a Markdown note

In a Snippet note

For tests

• Appears appropriate word/letter count on Markdown Note
• Not appear on Snippet Note
• Not appear on Trash

note

The word count is not supported in Japanese and Chinese.

[BoostnoteBot]

Be sure to be changed browser/main/Detail/SnippetNoteDetail.js.

[kazup01]

LGTM