Field editor review fixes

[rchristie]

• Coordinate system doesn't allow focus to be edited for prolate/oblate spheroidal.
• Allow coordinate system type & focus to be set for any field type.
• Derivative lists source field as "Coordinate field", should just be "Source field".
• Setting field to unmanaged if not in use does not destroy field as expected. How is it being maintained?
• Recommend Changing text "Add..." to "Define field type..." to avoid confusion with field type "Add"
• Field name should trim leading and trailing whitespace? Possibly repeat internal whitespace?
• Field Edge Discontinuity doesn't display measure and conditional field after creation.
• Mesh Integral field Number of Points should initially show default value 1, but allows for comma separated list of numbers of points in each xi direction; list is never shown after creation, only first number in it.
• Mesh Integral field Has parameter "Search Mesh", should just be "Mesh".
• Find mesh location field no longer shows additional parameters after creation.
• Nodeset operators sum etc. Nodeset should list datapoints/nodes/all node group field names. Currently lacking group names but also includes "Points" domain which doesn't exist and causes an error if attempt to use.
• Projection field "Source field 2" needs to be labelled "Projection matrix field".
• Long lists of constant values are not visible until field editor is made wider; maybe need horizontal scroll as well?
• Time value field should list timekeeper as "default" not "Available". Can use a one-item combo box.
• Vector coordinate transformation should list 2nd field as "Coordinate field" not "Source field 2", but does not list second field after creation (but field is serialised correctly).
• Apply field must be able apply source field in evaluate region which has zero or more arguments. Should only be able to select and bind to arguments that the source field actually depends on. Current implementation allows exactly one binding and can bind to any argument in the evaluate region regardless of whether source field depends on it. Zero argument is used for spatially constant fields. Two arguments is used for an arbitrary binary operator.
• Allow editing field type-specific parameters for MeshIntegral, FindMeshLocation, Apply, IsOnFace, NodeValue, EdgeDiscontinuity and possibly other fields.