Backend: generate best matching free room

# Feature
Given a list of building IDs, a date and a time range, return all of the rooms free during that time, both fully available and partially available.

## Example Format
Parameters:
- List of Building ID's
- Date
- Start Time
- End Time

Return:
- List of rooms that best match the time period

# Acceptance criteria
## Base Use
- Input: A list of valid Building ID's
- Output: A list of best matching rooms within those building id's and the times they are available within the start-to-end period