Merge pull request #1214 from blazetopher/gap_fill

Adds support for filling data gaps
Adds function for repairing temporal geometry

Exposes AbstractCoverage.repair_temporal_geometry via DirectCoverageAccess - allows an operator to \'repair\' the temporal geometry of a coverage by removing duplicates and reordering out-of-order timesteps

Adds test_repair_temporal_geometry to TestDirectCoverageAccess

Bumps coverage-model submodule