Throttling some ComCat API requests to avoid error

Recently ComCat has started issuing "too many requests" errors, due to overly enthusiastic users of the system. This release adds a throttle to the speed of multiple API requests to avoid running into those errors.

Cleaned up code to remove deprecation warnings

Merge pull request #255 from mhearne-usgs/appendfix

Replaced instances of deprecated dataframe.append with other methods …

Fixed bug in dataframes for moment tensors

Merge pull request #254 from mhearne-usgs/momentfix

Fixed issues with moment tensor products not displaying if strike/dip/rake values not filled in.

Bug fix in geteventhist ShakeMap output

Now correctly reporting number of instrumented/dyfi stations.

Fixes to DYFI dataframes

Merge pull request #249 from mhearne-usgs/dyfifix

Cleaning up code to handle older column names in DYFI cdi_geo.txt files

Fix to handle shakemap version numbers that are not integer

Merge pull request #248 from mhearne-usgs/intfix

Trapping for non-int version numbers in shakemap products

Fixed issue for geteventhist when ShakeMaps have no MMI values

Merge pull request #246 from mhearne-usgs/histfix

Fixed bug in shakemap history code

Added review status to origin output

Merge pull request #242 from mhearne-usgs/reviewfix

Added review status to origin description

Fixed issue when moment tensors have no content

Merge pull request #241 from mhearne-usgs/floatfix

Fixing moment tensors which have no content. Why these exist is unknown.

Bug fix in geteventhist

Merge pull request #240 from mhearne-usgs/stationfix

Fixing issue when a shakemap is missing station list