renamed getDeactivationReason to handleDeactivation in js
only add deactivation_reason param if it isn't null
only deactivate equipment object if deactivation_reason param exists
added overbooked check to make_deactivate_btn method
ensured that the deactivation reason warning only showed when appropriate
made cancellation handling better
refactored javascript conditional
made controller logic stricter
fixed whitespace in warning
Merge pull request #1026 from YaleSTC/983_deactivation_warning

resolves #983, deactivation warning