Error messages for Special:PageMigration

Basic error handling for Special:PageMigration. Errors arising when page does not
exist, no edit by FuzzyBot on the given pagename, absence of old translations have
been handled.

Bug: 65933
Change-Id: I4d6d17eb9f22930f5ada99f55c06dd8067adffbc
Merge "Error messages for Special:PageMigration"