Allow schema changes

[sebgie]

closes #2354
refs #1641

• added addUnique()
• added dropUnique()
• added addColumn() -> needed for Feature Request: User email address hide publicly #2330
• updated knex to 0.6.9
• changed schema.js
• further cleanup of the migrations module
• dropColumn() is missing due to lack of knex support

[tgriesser]

I'm scratching my head wondering how this actually works without bumping bookshelf. There were huge internal changes between knex 0.5 and knex 0.6 which Bookshelf 0.6 relied on for anything related to relations.

Also, there was a huge regression around memoizing column names in 0.6 -> 0.6.9 that was causing the test-suite to fail for me when starting from a fresh ghost repo (fixed in 0.6.10, but I'm not sure why they weren't showing up...)

[tgriesser]

Oh, nevermind, I know why, it's because bookshelf was installing it's own copy of knex locally to match the dependency version in bookshelf, and because you're not currently requiring it, initializing and passing into bookshelf (which will be required going forward), the version bump in this PR doesn't actually do anything with regards to knex.

[sebgie]

Updated :-)