Changed channels graphql query to use filter, added eventName and locationName filters

graphql/schema/types/channel.graphql

@@ -16,6 +16,18 @@ type Channel {
   locationName: String
 }
 
+# Filters for the channels query
+input ChannelsFilter {
+  # Filter to either logged or unlogged channels
+  logged: Boolean
+
+  # Filter by event name
+  eventName: String
+
+  # Filter by location name
+  locationName: String
+}
+
 input ChannelAddInput {
   # The channel's name
   name: String!