Djw 20 add edit delete timing windows existing observations

[DJWalker42]

• add, edit and delete TimingWindows in existing Observations
• able to change the Target and TechnicalGoal in existing Observations
• disable the "Observation type" Select input for an existing Observation
• use DateProvider around DateTimePickers to use timezone: UTC
• justify "centre" the "Add" new observation and the "Add" new timing window buttons

New Issues:

• On changing the target of an existing Observation i.e., selecting a new target id and pressing "Save", the "view/edit" modal closes; it shouldn't do that and I don't know why it does. Editing any other value does not close the modal as programmed.
• There's no API call to update the "intended use" of a Calibration Observation.

[AllanEngland]

I've had a good play around with this and it seems to work well, I'll merge in it now.

However, I find it a touch confusing that save has to be pressed when a new timing window is added, but not when one is been deleted. It makes sense (technically) given the flow of operations, but I'm sure there's a better way for the user to experience this - I don't yet know what that is, so will put some thought in for a future suggestion.