Add search event

Add the possibility to send search event to UNOMI.

The fields of the form should be added to the flattenedProperties of the event to avoid to create mappings for the fields.

The event should have the following structure to properties field of the event:

{
    originForm: The form name,
    language: The language,
    keyword: The search term,
    origin: The page where is located the form
}

In the tracker:
Add a function to help to build search events