update lower bound of modules

[disktnk]

To follow Flask 1.0.2, drop 0.12.2 or older. Current ChainerUI supports Flask 0.12.2, but there are some API change between 1.0.x and 0.12.x, so from next release, ChainerUI depends on Flask 1.x.

Using this opportunity, we update lower bound of module version.

• Flask: see the above
• sqlalchemy
  • released 1.2.x, but ChainerUI follows 1.1.x
• alembic: use latest 1.0.0
• gevent
  • released 1.3.x, but ChainerUI follows 1.2.x
• APScheduler
  • removed, not used

[gky360]

LGTM!