Creation of Search Engine module

[mageirakos]

Motivation

There is a need to create a module to handle all of our searching/querying needs.
This module will hold a SearchEngineFactory and have any classes related our requirements.

Modification

1. An FAQSearchEngine that looks at the FAQ Table
2. A QuestionSearchEngine that looks at previous Questions asked inside of emails. Thus, moving forward with their context perhaps we can answer the current query. This can be done for both emails and issues if we end up fetching issue data and parsing that as well ( related to #5 )
3. A DocumentationSearchEngine which has Rucio's documentation indexed and is used when querying simple questions the user asks whose answer might exist under our documentation

[mageirakos]

If the FAQ table has not been created in due time, this issue might close and a new enhancement issue to add the FAQSearchEngine will open

[mageirakos]

If the FAQ table has not been created in due time, this issue might close and a new enhancement issue to add the FAQSearchEngine will open

On the implementation the FAQSearchEngine is basically the SearchEngine for Questions, which returns most similar question+context. But in the FAQ case the actuall context is previously supervised and is the whole answer.
So whichever module handles the answer generation/detection/ranking is confident on this result and should return it without further checks.
Thus, there is no need to open an enhancement issue