Update availibility migration and add basic crud

data/migrations/20200502193443_availibility.js

@@ -1,6 +1,8 @@
 exports.up = (knex) => {
 	return knex.schema.createTable('availibility', (table) => {
 		table.increments('id').primary();
+
+		// Reference to participant composite primary key
 		table.uuid('meeting_id').unsigned();
 		table.integer('account_id').unsigned();
 		table
@@ -8,10 +10,10 @@ exports.up = (knex) => {
 			.references(['account_id', 'meeting_id'])
 			.on('participant')
 			.onDelete('cascade');
+
+		table.integer('possible_date_id');
 		table
-			.integer('possible_date_id')
-			.unsigned()
-			.notNullable()
+			.foreign('possible_date_id')
 			.references('possible_date.id')
 			.onDelete('cascade');
 		table.boolean('preference').notNullable();