Add support for location in audit

[yanokwa]

Building on the issue at getodk/xforms-spec#219 and PR at https://github.com/opendatakit/xforms-spec/pull/221/files, we should add support for locations in the audit log.

My rough proposal is

• Add support for three parameters for audit questions (location-priority, location-min-interval, location-max-age) (note, we don't include the odk:)
• If one of the parameters are entered, then all three are required
• priority has four potential values: no-power, low-power, balanced, or high-accuracy
• max-age and min-interval are positive integers. max-age >= min-interval

Sample output looks like:

<bind nodeset="/orx:meta/orx:audit" type="binary" 
           odk:location-priority="balanced" odk:location-min-interval="10" odk:location-max-age="60" />

[yanokwa]

@KeynesYouDigIt This something you'd be willing to take on?

[ukanga]

This is closed by #260

[KeynesYouDigIt]

@yanokwa Sorry about that! missed your mention somehow.