Prevent confirmation of conflicting reservations

[shubhpatel108]

Presently, the admin can confirm 2 reservations on exactly the same or overlapping time. This could be allowed only if the requesters are same or/and after warning the admin about the conflict.

[jessyurko]

Duplicate of #65

[shubhpatel108]

#65 prevents a user from requesting, this issue aims at preventing their confirmation by admin. Reopening.
I think this make more sense as admin may select the one with the highest priority among the conflicting ones.

[arkokoley]

Solution of #65 makes this issue redundant. Will close this when #209 is merged.