Add RawMask.swift

Just adds an &== operator to return whether the bitwise-and of two
RawRepresentables yields the RHS value.
(e.g., same as `(foo & bar) == bar`)
Add Array.withoutIndices extension.

Simply returns an array sans the indices in the given indexSet, because
NSArray has this but Swift's Array doesn't.
rulesData: Implement drag/drop for the rules list.

More or less a straight port of the code from Schemer.
document: Allow selection of multiple rule rows.
ruleController: Set dragging properties.