Braille/Liblouis 3: provide a way to detect and change table names if old tables are no longer included

[josephsl]

Hi,
Part of #6109:

As noted in the following LibLouis issue:
liblouis/liblouis#182

There might be instances where NVDA's own tables tuple may refer to deleted tables. If this happens, the following may result:

1. Braille Settings: no table seems to be selected. This is a minor thing (for about 99 percent of tables, table names are the same).
2. Runtime translation issues are noted due to the fact that some tables rely on other tables.

Thus it would be handy to provide the following migration strategy:

1. Add config checker in braille.initialize that reads in config.conf["braille"]["*Table"] key.
2. Based on the name of the file it read, look up a dictionary which tells NVDA the new filename for the given table.
3. Replace the old name with the new name.

Potential problems:

• What if no replacements are provided? In this case, tell users to specify the new table from braille settings.
• Do we know which tables are gone or renamed? We need to wait until LibLouis 3 beta comes out before proceeding.

The needed change(s) will be committed as part of #6109 branch (#6110 for PR). Comments are appreciated. Thanks.