There is no uniqueness for module's name

[kirill-tolochko]

Problem description

Module with the same name as existing module could be created

Step to reproduce

Steps to reproduce the behavior:

1. Create module, name it "Module"
2. Publish it
3. Click on "save as" on the edit page of this module
4. Save it as "Module"

or

1. Create module, name it "Module"
2. Create another one module, call it "Module"

Expected behavior

In both cases user shouldn't be able to create modules with the same names

Actual behavior

User is able to create modules with the same name