- changes api using web sockets
- databases fetching using changes api, including disabled databases
- file systems dropdown using changes api
prevent subscribing twice to the same database for changes
don't show dropdown when there are no databases except the system database
- changes api applied to databases page
- changes api applied to counters page
- changes api applied to shell (drop down lists)
- hide/show dropdown according to data length
removed unnecessary
small css shell.html fix
refresh button fixed
Merge branch 'RavenDB-2404' of https://github.com/grisha-kotler/ravendb into RavenDB-2406

Conflicts:
	Raven.Studio.Html5/App/viewmodels/shell.ts
merged with grishas changes