Configurable filters -- view a subset of sites

[narc0tiq]

Currently sites are divided into two groups: those which have less than 10% of their initial ore remaining, and all the others. This corresponds to the minimized/maximized state of the YARM list.

For the future, I'd like to change that to a set of configurable filters:

• less than X% remaining
• sites with estimated time to depletion less than X minutes (@tivec))
• idle sites (not including untapped sites (at 100% remaining)) (@tivec)
• sites with miners that no longer have anything under them
• active sites (being mined, i.e., non-zero ore-per-minute/miners are present) (@tivec)
• sites with [specific ore] -- which can include a virtual "total" site summarizing all the data (@cpw)
• all sites with warning conditions (i.e., union of the first two filters)
• all sites

Where applicable, the filters' numbers should be configurable, with separate values for finite (e.g., ore) and infinite (e.g., oil) resource sites, as the same numbers don't usually make sense for both.

[narc0tiq]

Some progress was made in v0.8 -- instead of the expando, there are now filters, they're just not configurable yet.