Remove two unmaintained vendor packages `i18n` and `paginater`. Changes:
* Rewrite `i18n` package with a more clear fallback mechanism. Fix an unstable `Tr` behavior, add more tests.
* Refactor the legacy `Paginater` to `Paginator`, test cases are kept unchanged.
Trivial enhancement (no breaking for end users):
* Use the first locale in LANGS setting option as the default, add a log to prevent from surprising users.
* display ui time with customize time location
* fix lint
* rename UILocation to DefaultUILocation
* move time related functions to modules/timeutil
* fix tests
* fix tests
* fix build
* fix swagger
wxiaoguang
Lunny Xiao
Tamal Saha