[Buildbot] #3187: add a 'slug' to masters so they can be referred to by name

[Buildbot trac]

#3187: add a 'slug' to masters so they can be referred to by name
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Reporter:  dustin       |      Owner:
    Type:  enhancement  |     Status:  new
Priority:  minor        |  Milestone:  0.9.+
 Version:  0.8.10       |   Keywords:
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 Blocks #2635.

 Add a new, automatically populated, unique identifier column - a slug - to
 the masters table, and allow users to specify that slug in URLs in place
 of `n:masterid`.

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Ticket URL: <http://trac.buildbot.net/ticket/3187>
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