Implement libchewing 0.9.0 features

[kanru]

• [x] Use chewing_ack to acknowledge output buffer
• [x] Support new input modes
• [x] Allow space key for pagination
• [x] Merge DOWN and SPACE key paging behavior
• [ ] Enable new option to disable fullwidth toggle key
• [ ] Enable new option to disable shift toggle key
• [ ] Workman layout
• [ ] Option to show notification about mode switches triggered by input
• [ ] Show libchewing version in setup about page