Add some generic x axis options

[DanielSank]

• log
• A few time formats
  • UTC, datetime, others(?)
  • referenced to user-supplied origin
  • "Pure time" with auto or manual selected units.
• I dunno, that's probably it.

[joshmutus]

relative to beginning? (make initial time zero)

[DanielSank]

Let me try to be more explicit. These are just ideas:

1. Data stored in UTC

   1. Show as datetime
   2. Show as difference from user supplied datetime, in either manually selected units or autoselected units. For example, hours, days, minutes relative to my supplied origin.

2. Data stored as a straight-up time, i.e. minutes hours. In the case, we probably just want to be able to adjust the origin and/or units.

Not sure if all of these are actually useful. Probably the UTC-->datetime one would be the most interesting.