Add source table

[robertdstein]

This PR adds a new table for WINTER sources. Fix #732, fix #734. From now onwards:

• Source Names are assigned using the source table. New candidates are crossmatched to this.
• Each candidate has a sourceid foreign key. Many candidates to one source.
• The sourcetable has an average position. The winter pipeline will retrieve the full history and then update the position in the source table accordingly.
• Databases are slightly reworked to reflect this. You can now do single spatial crossmatch, multiple spatial crossmatch, or query by parameters in the same way as images.
• History is now assigned by querying the candidate table for candidates sharing a sourceid, NOT via spatial coordinates.

This is a breaking change, and is somewhat decoupled from the migration of the existing database which we will need to implement. My preference would be to somehow create a clean candidate table and source table, and then reingest old candidates in sequence to assign names correctly. I am just worried it'll undercut all the candidate scanning done so far.

[virajkaram]

Approved, but I think we should maybe test the candidate naming before merging. Would it be feasible to add another image to the tests to make sure this is working ?

[coveralls]

Pull Request Test Coverage Report for Build 7938845778

Details

• 129 of 137 (94.16%) changed or added relevant lines in 20 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 86.425%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
mirar/processors/sources/namer.py	7	8	87.5%
mirar/processors/database/database_selector.py	33	35	94.29%
mirar/pipelines/winter/generator.py	22	27	81.48%

Files with Coverage Reduction	New Missed Lines	%
mirar/monitor/base_monitor.py	1	83.0%

Totals
Change from base Build 7920912710:	0.3%
Covered Lines:	10078
Relevant Lines:	11661

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💛 - Coveralls

[robertdstein]

Proposed way forward: create a clean candidate table and reingest. Rename old real bogus/candidate table.
Add CI test to winter, with just a source table being loaded to check history assignment.

[robertdstein]

@virajkaram I have confirmed that this does work by creating a dummy candidate, which leads to history/the correct name/ndet=2 in database.