Changes to the coverage model

```
c3908e8 Merge pull request #41 from oceanzus/refactor_hdf_metadata
fe288b0 Fixes coverage constructor bug Addresses issue when constructing
a coverage with an existing temporal domain of shape > 0
ea9833a Consolidates logging statements and removes unused commented
code.  Fixes test_create_multi_bricks.
eda4242 Updates insert_timesteps to call expand_domain only once.  Fixes
method by which external links are added to the master file.
d6cfdb3 Changes order of MasterManager initialization of the brick_tree.
4582431 Removes references to parameter_name in the brick_list.
48c3309 Isolates creation of virtual bricks from each parameter
initialization.
b0133be Adds sharing of domain objects
12bf2be Adds read_only flag to ParameterManager
37af78d Migrates brick metadata to master file.
c243cc7 Modifies method by which bricks are managed.  Initial trial.
```