Custom landsat date range

[kylebarron]

Might be best to provide a date range (of min 16 days, or just show a warning dialog if <16 days). Then not necessarily show a cloud cover slider, just automatically sort to have least cloud cover per pathrow.

You probably want a maximum date range, and maybe expose the option to have a "closest to date"/first/last options.

[kylebarron]

Closing as duplicate of #23