top_frontend translation for zh-cn
index translation for zh-cn
Merge branch 'i18n'
footer translation for zh-cn
Merge branch 'i18n'

Conflicts:
	application/views/footer.php
problem list translation for zh-cn
Merge branch 'i18n'
searchform translation for zh-cn
Merge branch 'i18n'

Conflicts:
	application/views/problem/searchform.php
problem search translation for zh-cn
Merge branch 'i18n'
problem show translation for zh-cn
Merge branch 'i18n'
fix nav-pills center in problem show
Merge branch 'layout'
hide hint and source when empty