Training: Add unit tests and change datatype of two columns

[blackcoder87]

Description

• Added unit tests.
• Changed datatype of two columns.
• Adjusted the training model.
• Adjusted the entrants model.

The columns "voice_server" and "game_server" don't need to be of type INT when they only should represent a boolean value.
Changed them to TINYINT.

`voice_server` TINYINT(1) NOT NULL DEFAULT 0,
`game_server` TINYINT(1) NOT NULL DEFAULT 0,

The id of a training model can never be 0 as it is a primary key in the trainings table.

`id` INT(11) NOT NULL AUTO_INCREMENT,

The id of the training and user id in the training_entrants table have a FKC to the respective columns of the training and user table. They can never have the value 0.

Type of change

• Bug fix (non-breaking change which fixes an issue)

This PR has been tested in the following browsers:

• Chrome
• Firefox
• Opera
• Edge