remove leveldb, use sqlite and unqlite. create migrator tool

lbrynet/core/sqlite_helpers.py

@@ -0,0 +1,20 @@
+import sqlite3
+from twisted.internet import task, reactor
+import logging
+
+
+def rerun_if_locked(f):
+
+    def rerun(err, *args, **kwargs):
+        if err.check(sqlite3.OperationalError) and err.value.message == "database is locked":
+            logging.warning("database was locked. rerunning %s with args %s, kwargs %s",
+                            str(f), str(args), str(kwargs))
+            return task.deferLater(reactor, 0, wrapper, *args, **kwargs)
+        return err
+
+    def wrapper(*args, **kwargs):
+        d = f(*args, **kwargs)
+        d.addErrback(rerun, *args, **kwargs)
+        return d
+
+    return wrapper