Make SvxAutocorrWordList explicitly non-copyable.

Change-Id: Idc056fd216bfe0b5e5c0285b1781b0658837f5a2
Apply pimpl to SvxAutocorrWordList.

And remove <set> and <boost/unordered_map.hpp> header includes from its
public header.

Change-Id: I7e748009f718f4195bec2348383df07dc67600cd