Resource management

[alex-eg]

Alpha milestone mentions following things:

• levels
• weapons
• player craft
• enemy craft[s?]
• enemy types
• enemy waves
• behavioural patterns -- as I understand, it's movement and attack patterns, which are pre-defined and bound to each wave
• boss
• [optional] pick-ups
• sounds
• music

While not all of them have to have an editor, we must decide on how to create, use and modify all of them, in terms of in-game engine entities.