Migrate to yarn and upgrade libs

1. Migrate bower to yarn for dependency management.
2. Remove vghks mode switch and standard dev setting.
3. Change export excel format to xlsx, due to lib upgrade.
4. Add vghks style in exporting excel.
5. Fix event dialog behavior. (#55)

v0.2.5

1. Change event order: duty, holiday, non-duty. (#52)
2. Upgrade dependency packages.
3. Use iso week, starting from Monday.
4. Can calculate week work hours with pm off.
5. Show alert if cont workday interval is more than 12.

0.2.4: Release Note

1. Show only the DAY instead of MONTH/DAY in 1-month mode. (#51)
2. Confirm that there is no friday determination error. (#47)