Remove playfromHTMLtag service hook

This one is also the same from service to service, so its functionality
can be moved to the main module.
Remove playfromtag hook from services

This is now handled, like the former HTML tag hook, directly through the
play callable in the given service module.
Store all VOICES as list-of-tuples

Using a consistent data type for these will allow some future
efficiencies with writing the service modules.
Alphabetize and remove duplicates in SAPI 5

This is done via a regular set, sorted case-insensitively.
Remove unused TTS_record function

The services' record implementations are accessed elsewhere.
Removed unneeded globals declaration

Variable names only need to be declared if the function in question will
be changing their values.
Import services without file system crawling

This updates the services package's init module to expose the services,
and uses that instead. In the future, the entire initialization bit
might move into that init module instead of being part of the main
module in the root of the add-on.
Fix default voice variable typo in SAPI 5

This allows the voice dropdown to persist properly.