Contracts should be case locked.

[JeffWScott]

Describe the bug
Contracts are not case locked, so "currency" and "Currency" would be stored as two different contracts. That's a security risk.

To Reproduce
Steps to reproduce the behavior:

1. Submit a contract as "testing"
2. Submit another as "Testing"
3. See both exists on BC.

Expected behavior
contracts should be converted to upper and lower and compared for duplicate names.

[StuartFarmer]

Calling str.lower will fix this. We can also restrict the names to be ASCII only, a certain length, and prepend a prefix to prevent collisions with Python keywords.

While -> while -> c_while # Add c_ prefix?
123hElLo -> should fail
Hi^^^%%@@ -> should fail