Use native Magento indexer functionality for Algolia search.

Sylvain, the pull request contains significant improvements for the existing functionality. The main goal of this improvement is to use native Magento indexer functionality for Algolia search. It was added to System > Index Management. Build in indexer system is much more flexible rather than trying to check whether indexing is required using observers for product/category save etc.
All changes were tested and seems pretty stable.
Also improved categories proxy to exclude category from the active categories list if any parent category is inactive.
Also removed store code prefix form object names as index name includes store code. So "default_product_111" object name is now "product_111".
Because of the object id change I suggest for testing to clean existing indexes.
There is no conflict between "Catalog Search Index" and "Algolia Search Index". They even can be used in parallel!
Also added configuration to seperate popup window on frontend and using Algolia search for default catalog search and updating index:http://screencast.com/t/Ig3iiojSL2LT
There are a lot of changes so combined all of the to a single commit after everything was done.

During merge there will be a conflict with Algolia_Algoliasearch_Helper_Data. A lot of changes were added to this file. The new file can be used instead of the old one.