Lazuli

- Add `currency` property to Character
- The `currency` property is a dictionary of all the currencies (e.g. NX) associated with the account that contains the character.
- Dictionary keys: `mesos`, `nx`, `maplepoints`, `vp`, `dp`
- Add `characters` & `free_char_slots` properties to Account
- `characters` is a list of the IGNs of all the characters in the account
- `free_char_slots` is an integer representing the number of free character slots in the account

- Make the use of pre-underscores in variables consistent
- Remove accessor for variables like _database_config
- These are now always be used with the pre-underscore internally
- Reason: These variables should NOT be accessed manually when using Lazuli's API
- These changes are not considered breaking, since the removed properties weren't intended to be manually accessed in the first place

- Fixed char image method in Character
- Previously broken due to faulty refactor of Inventory instantiation

- Made Inventory lazy-instantiation by:
- refactoring to a method in Lazuli, instead of Character
- Update unit test WRT breaking API changes

- Add getter methods that return all attributes together
- Made Inventory instantiation more efficient by reducing SQL calls

- Perform general linting