pass in value directly in created_at default value

in order to stay compatiable with sqlite
cmd module refine.

1. remove session protection config as it's not commonly used.
2. include upgrade in every serve.
remove psycopg2 requirement.

it only needed for postgresql database
change defaults not enable oauth at all
auto find category.

1. moved category to extension cls.
2. no need to manually input category any more.
rawgithub is better than raw.github
no need to show uuid. it's in url already.