Move InfluxDBStore into experimental subpackage; hide Dashboard for now.

[slimsag]

We've seen that InfluxDBStore hasn't lived up to our expectations, and have been encountering performance problems (particularly RAM usage problems) with it. It has been the source of a great amount of instability within Appdash, and while it's likely to improve in the future, the current plan is to move it into an experimental subpackage and potentially pick it back up in the future (though there are no current plans to do so).

• Fix appdash serve (assets not served properly)
• Do not display/serve Dashboard page except when using InfluxDBStore (not the default).
• Move InfluxDBStore into experimental subpackage.
• Fix #150
• FIx #163

Users will need to update according to the following table:

Before	After
appdash.InfluxDBAdminUser	influxdbstore.AdminUser
appdash.InfluxDBRetentionPolicy	influxdbstore.RetentionPolicy
appdash.InfluxDBConfig	influxdbstore.Config
appdash.NewInfluxDBConfig	influxdbstore.NewConfig
appdash.NewInfluxDBStore	influxdbstore.New
appdash.InfluxDBStore	influxdbstore.Store

[keegancsmith]

glad to see the removal of vendor!

also LGTM