Add support for custom dimensions.
Add units attribute for validation purposes.

For now this is hard-coded to be empty, as code to make it configurable would conflict with the pending elevation units patch. This can be changed as soon as that patch is accepted.
Confine DIM_ prefix processing to core WMS handling code, so that the reader and other protocols use the original (unprefixed) dimension name.
Adding GUI for custom raster dimensions, and handling units and unit symbols
[GEOS-5218] Allow the WMS elevation units to be editable

[GEOS-5218] set default units for elevation dimension to EPSG:5030
Adding a prefix for custom dimensions in the metadata map to avoid collisions with other params in the metadata map
[GEOS-5539] Support raster custom dimensions generated at runtime
Fixing dynamic dimension tests after changes to coverage delegate handlers
improved custom dimensions management
fixing custom dimensions management
fix ConcurrentModificationException when removing unsupported dimensions
backport tests to 2.2.x