Depth first

[dkirkby]

This PR adds the following features:

• Implement an optional depth-first survey strategy (via rules-depth.yaml)
• Add progress columns to track fiber assignment and planning (fixes tools for when to rerun fiber assignment #18)
• Add set_value() method for config nodes (fixes update/document how to change Configuration object parameters #49)
• Adds E(B-V) column to progress (fixes Progress is missing some fields #54)

[coveralls]

Coverage decreased (-0.1%) to 56.647% when pulling f6bd910 on depth_first into fc4f794 on master.

[coveralls]

Coverage decreased (-0.1%) to 56.636% when pulling 37071ad on depth_first into fc4f794 on master.

[dkirkby]

I am still working on an issue with surveymovie so this is not ready to merge yet.

[dkirkby]

This is ready to merge now.

[coveralls]

Coverage decreased (-0.1%) to 56.636% when pulling ebaf5de on depth_first into fc4f794 on master.

[coveralls]

Coverage decreased (-0.2%) to 56.595% when pulling 0d51d17 on depth_first into fc4f794 on master.

[sbailey]

Regarding the progress columns: these are the "covered", "available", and "planned" columns? They are integer days since start of survey (not dates or MJDs)? For the record could you define (again) the difference between "available" and "planned"? i.e. what's the recipe for knowing when to run fiber assignment on what tiles?

Clarifying: whether a tile is "covered" or not depends upon the rules file, correct? Or is it just "all tiles from previous layers that cover this tile have now been observed" regardless of whether the rules file says you should wait for them or not?

Code looks fine to merge, but I'd like to document how to use those progress columns.

[sbailey]

I now see that you defined when to run fiberassignment in issue #24:

adds a column available to the progress fits file that records the day number (defined by a new desisurvey.utils.day_number() function) on which the fibers for each tile are assigned. With the default monthly fiber-assignment cadence, this will always fall on the day closest to a full moon.

[dkirkby]

Clarifying: whether a tile is "covered" or not depends upon the rules file, correct?

Correct. In particular, this section of config.yaml determines which passes are pre-requisites for each pass (P0-3 = DARK, P4 = GRAY, P5-7 = BRIGHT):

fiber_assignment_order:
    P1: P0
    P2: P0+P1
    P3: P0+P1
    P6: P5
    P7: P5+P6

I decided to treat this as config, rather than hardcoded, since we currently treat P3 differently from other DARK layers. Also, note that:

P1: P0
P2: P0+P1

is subtly different from:

P1: P0
P2: P1

(but I think this only matters at the edges).