Normalise batch file line endings to CRLF
Add new tools folder with sqlite3 and recoverdb

Import the source of the 'recoverdb' utility (which attempts to repair
corrupted databases) into a new tools folder.
Also add a copy of the sqlite3 command line Windows binary which is part
of the recoverdb utility and is also generally useful for working with the
application database.
Check databases are not corrupt at startup

After opening connections to the template database, the user database
and the search index database (all at startup), execute a pragma
integrity_check command to test if the sqlite database is valid or has
become corrupted.

If the template or user databases are corrupt then refuse to start and
show a message to the user (in the case of the user db with an option to
open the help page about this).  With the search index, just delete and
re-create it automatically.

Resolves #191.