Don't make a query to fetch each answer of a response separately. Fetch them all at once.

Conflicts:

	app/views/responses/index.xlsx.axlsx
Eager loading choices along with answers while downloading excel.

Conflicts:

	app/views/responses/index.xlsx.axlsx
Eager load options along with choices while downloading excel foe a survey.

Conflicts:

	app/views/responses/index.xlsx.axlsx
Check for an existing answer before create using mobile_id only if mobile_id is passed with the params in API::ResponsesController