Revert "Merge branch 'like' into develop"

This reverts commit 22707e89052924f07a1f93b985fc79a3dfa35368, reversing
changes made to 1be5a7f56c16593c367f7f6cd3a1ff7f2780c74e.
Remove password_digest from users
Add like model

[Issue #21] https://github.com/ideaegg/ideaegg/issues/21
Add counter_cache to likes

[Issue #21] https://github.com/ideaegg/ideaegg/issues/21
Set default_value to likes_count

[Issue #21] https://github.com/ideaegg/ideaegg/issues/21

- Idea
- User
Add like

[Issue #21] https://github.com/ideaegg/ideaegg/issues/21