Contacts part of the database

[ericcornelissen]

• Relevant Issues: #27

• Related Pull Requests: n/a

• • *

What

With this pull request a GSON implementation of the database will be added which, for now, is capable of:

• [x] Create a new contact in the database (i.e. an entry with public key and name).
• [x] Modify a contact in the database (i.e. change the name).
• [x] Delete a contact from the database (i.e. remove the entry, key+name, completely).
• [x] Get a list of all contacts from the database (i.e. a list of the names of all contacts).
• [x] Get a specific contact from the database (i.e. all information about that contact, name+key).

Why

We want to store the contacts on the phone so they can be viewed/used at a later point in time

How

The database adapter in the PR is implemented using Google's gson, as a result the database is implemented in JSON files.

Alternative implementation

We have considered using other simple text-based database implementation (such as .csv) but felt that a JSON implementation is the right combination of simple and extensible.

Notes

• The ExampleUnitTest has been removed as this is the first PR with actual unit tests.
• The class KeyAdapter in the modules/database package is needed to convert the arbitrary key representation in the database to an actual key POJO implementing the IKey interface.
• Each IKey implementing class needs a getType() method so the KeyAdapter can use the type to figure out what instance of IKey it must create when reading the database.
• This PR is somewhat related to #56 as there is an issue with the ServiceLocator (this also exists in develop), so there might be some issues but these will be fixed soon

[TheBonheurs]

@ericcornelissen Here is the link, I also had made a comment about it in #59 https://github.com/ericcornelissen/NervousFish/pull/59/files/999f4c96e64c457960824fb15a67f99fc4b2106e#diff-c5abb3af466f8817cb122941c6e88cb4R141