chore(release): Starting v0.12.0-SNAPSHOT
fix(dropdown): remove `C` restrictions to avoid conflicts

Fixes #2156

Closes #2170

BREAKING CHANGE: Both `dropdown` and `dropdown-toggle` are only attribute directives

Before:
  ```html
  <button class="dropdown-toggle" ...>
  ```
  After:
  ```html
  <button class="dropdown-toggle" dropdown-toggle ...>
  ```