GSoC History API including sqlite history adapter

The History API has been created to drive all message handling in purple3. It will be used to update existing messages for edits, reactions, pinning, read/deliver receipts, etc. The API uses an adapter pattern, to abstract out backends, but provides a SQLite3 backend by default.

It also provides search capabilities using a custom query language that can easily be expanded over time. It will be use by both the end user to search messages and the frontends to implement features like a pinned messages button. A command line utility is also provided for searching outside of the program itself.

## Remaining Items

**These all will most likely be done by the Pidgin core team after GSoC when we figure out exactly how to solve them.**

Need to store database in purple config directory
* Gary has spent some time looking at this and it looks like the purple-history cli will need to become a purple-ui to make this work write as in the future other adapters will be plugins.

Other things to consider:
- For simplicity, the SqliteHistoryAdapter is parsing the query itself, but for consistency having `PurpleHistoryAdapter` parse the query and pass tokens to the subclass might be something we want to do.

Testing Done:
## Unit Tests
History Manager
History Adapter

## Integration Tests
purplehistorycore created for integration tests.
PurpleSqliteHistoryAdapter functionality tested:
- Creates proper db schema
- Writes logs
- Reads logs
- Queries using query language
- Deletes using query language

Bugs closed: PIDGIN-17526, PIDGIN-17532, PIDGIN-17533, PIDGIN-17534

Reviewed at https://reviews.imfreedom.org/r/877/