"Played" indicator

[dwhinham]

Add a feature to the file browser to show which songs have already have been played in this session, a bit like Traktor.

This could be as simple as a small icon next to played songs.

The indicators should survive when the user navigates up and down the file system hierarchy.

Idea for implementation:

• Implement a fast hashing function (e.g. Pearson hashing) that can scan a module header and create a unique hash code based on its file name, file size, song title, and sample names (n.b. whole module header).
• For every song that has been played for more than $SOME_AMOUNT_OF patterns, add its hash into a global in-memory "played" list. This could be a fixed length, or dynamically-growing.
• When refreshing the file browser, hash each song being scanned. If the resulting hash code is in the "played" list, draw its "played" icon in the file browser.