Issue #232, initial similarity calculation algorithm.

Based on Jaccard similarity of the tag sets only. Al bakeya tatba3.
Calculate idea similarity on save.
Add similar_ideas relation to the Idea model.
Add default ordering to the Similarity model.

order by similarity
Add similar ideas partial.
Turn on library autoloading
Revamp the similarity index algorithm.
Tune the similarity calculation model.

Add lambda values to calculate functions of each component.
SimilarityEngine: tune model again and load necessary idea data on creation.
SimilarityEngine: add tests

100% coverage
SimilarityEngine: add manual rebuild routine.

Automatic calculation should be turned off during DB population or it will take
forever.
Turn off similarity calculation during db:populate
SimilarityEngine: remove stale comment.
Merge branch 'master' of github.com:DevYah/coolsoft-13 into C1_mnzaki_#232_similar_ideas

Conflicts:
	Idearator/app/models/idea.rb
SimilarityEngine: do not add an idea as a similar idea to itself
SimilarityEngine: don't delete all records while rebuilding
SimilarityEngine: add conditions on Idea.similar_ideas

Similarity must be at least 5, limit is 5.
Update the similar ideas partial.

Add span4.
Don't display if there are no similar ideas.
Use num_votes.
Render the similar_ideas partial in the ideas view.

Does not look very clean, but it's functional for now.
Fixed documentation typo