Add tree width options

[pgaskin]

closes #990
closes #772

[pgaskin]

A few notes:

• I'm not completely familiar with the UI code, so I'm not 100% sure this doesn't cause issues elsewhere, but it seems to work fine right now.
• Since I'm using an int between 1 and 100, we lose precision (it used to divide by 3), but this is mostly irrelevant since terminal windows aren't wide enough to make this have a significant effect. If this is an issue, I could parse it as a double or a fraction with a numerator/denominator instead.
• At high percentages (e.g. 99%) with small windows, the text on the right pane may spill over to the next line since the headers don't shrink. If this is an issue, I could set a minimum width for the right pane, but it isn't really usable when it's that small in the first place.

[pgaskin]

Tested tree/library/playlist views, mouse events, resizing window, setting window size from rc/autosave/command-line/remote.

[nefthy]

• I'm not completely familiar with the UI code, so I'm not 100% sure this doesn't cause issues elsewhere, but it seems to work fine right now.

IMO it's better to handle the width in columns since that is the basic underlying unit.'

[pgaskin]

What do you think of renaming it to tree_width and making it accept either a fixed value (later constrained to the max width of the window) or a percentage (if there's a percent sign at the end)?

[nefthy]

sounds good

[pgaskin]

Actually, I think I have a better idea: adding an optional tree_width_max option to limit the maximum width, and increasing the maximum tree_width_percent to 100%. This will allow both: setting a fixed size and still making it work properly at smaller window sizes, limiting the size only on large window sizes, and keeping the old behaviour.

[nefthy]

Also a good option.

[pgaskin]

Tested tree/library/playlist views, mouse events, resizing window, setting window size from rc/autosave/command-line/remote with:

• tree_width_percent=100 tree_width_max=60
• tree_width_percent=33 tree_width_max=60
• tree_width_percent=33 tree_width_max=0
• tree_width_percent=1 tree_width_max=9999

[pgaskin]

@nefthy, this is ready for review now.

[pgaskin]

I took a closer look at the code, and I'm now fairly certain this won't cause issues elsewhere.

[nefthy]

Looks good, but please rebase, as there is a conflict with another merge

[nefthy]

thanks