Add support for REST services

jirikadlec2[CodePlex]
We need to add support for REST services in the Download plugin:
1) Recognizing a valid data sites layer:
If a point layer has the columns:
SiteCode, VarCode, StartDate, EndDate, WaterMLUri, then it is a valid REST-enabled Data Sites layer. This layer should have the pop-up functionality enabled.

2) Downloading the data in DownloadManager: If the layer has a WaterMLUri column, then the download manager should get the xml from this Url instead of using WaterOneFlowClient / SOAP. For example,

http://midgewater.twdb.state.tx.us/tpwd/GetValues?location=TPWD:275107_970132variable=TPWD:seawater_salinitystartDate={time:start}endDate={time:end}

is a valid WaterML REST uri. The tokens {time:start} and {time:end} should be replaced by the values of the StartTime and EndTime columns in this case.

Attached is a shapefile that has the WaterMLUri column.

Start by locating the Download plugin, DownloadManager, and WaterOneFlowClient, then inspect how layer columns are recognized and how downloads are selected. Use the attached shapefile as the REST-enabled layer example; done means the specified columns enable pop-ups and WaterMLUri downloads retrieve XML with the time tokens replaced from the layer values.

Written by the indexing model from the issue text.