Fix projectiles rendering

[pkulev]

Closes issue(s): [ #47 ]

Description of the changes:

render:

• remove obsolete Renderer class
• make render_objects sort objects by render_priority class attribute
• do not render spaces

ingame:

• add to state temporary function to add game objects

  This game objects can be compound and consist of several renderable objects. In order to unfreeze further development this changes contain several dirty passages. I will remove them when I finish the appropriate object system.

ship and game: remove unused imports and settings, make Ship compound

 compound = True in class means that this class implements get_renderable_objects()
 function. This is crutch for projectile rendering, will be replaced by proper
 game object system in I hope near and bright future after alpha release.

• What's new: use render_priority in render_objects function
• Fixes:
• Refactoring: remove Renderer class and it's usage

Reviewers: [ @taptap ]

Task list:

• [x] submit pull request
• [x] review
• [x] testing
• [x] fixes after review, squashing, rebasing to master

[codecov-io]

Current coverage is 55.81% (diff: 7.69%)

Merging #48 into master will increase coverage by 0.43%

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  Methods           0          0          
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- Hits            958        955     -3   
+ Misses          772        756    -16   
  Partials          0          0          

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