apps: rework portBindings

ports is REST API input . Map of env var to the host port
portBinding is the database structure. Map of env var to host port, count, type etc

also, rename portCount -> count in various places to keep things consistent

migrations/schema.sql

@@ -118,7 +118,7 @@ CREATE TABLE IF NOT EXISTS appPortBindings(
     type VARCHAR(8) NOT NULL DEFAULT "tcp",
     environmentVariable VARCHAR(128) NOT NULL,
     appId VARCHAR(128) NOT NULL,
-    count INTEGER DEFAULT 1,
+    count INTEGER NOT NULL DEFAULT 1,
     FOREIGN KEY(appId) REFERENCES apps(id),
     PRIMARY KEY(hostPort));