Fixes #142

• added option to add list of station codes in Stations endpoint
• in GetStations, if inlcudeStats is false but there is a variableTypeList provided it will include those variables in the response

Example (will only return sites with drnarea):

• http://localhost:53812/stations?codes=01651800,01649000&variableTypes=1

Thought about adding an includeVariables along with an includeStats, but was a little worried about repercussions. For example, say someone is using includeStats=true somewhere but is using it to grab variables not stats. Then we change the endpoint those variables would no longer be returned because they don't have includeVariables=true in their request.

Also, I wasn't sure if just updating the appsetting.json would update the docs. I looked in https://code.usgs.gov/StreamStats/web-services-and-apis/GageStatsServices/-/tree/dev/Docs/Stations, but it didn't seem to have any text for 'Parameters'. I only found the parameter text in the appsetting.json. We may just have to try deploying & see if they update?