Added SQLite support for PasswordType

[frol]

This change fixes the issue of column type mismatch on SQLite as VARBINARY type fallbacks to NUMERIC, and in the end, Alembic always detects changes in my project:

Detected type change from NUMERIC(precision=128) to PasswordType(max_length=128) on 'user.password'

According to this reply on SQLAlchemy support forum, sa.VARBINARY is not a good fallback, but I have no idea on how would a correct implementation look like, so I only added SQLite support.

Originally, I thought my problem is reported in #106, but it turned out to be another not quite closely related issue.

#233 is another enhancement for PasswordType, which, in fact, solves #106.

[frol]

Weird! SQLite used NUMERIC type as a fallback for the column when it used to be VARBINARY, but once I tried to set it as NUMERIC on the Python side, it broke... Anyway, I didn't feel like NUMERIC is the proper type for PasswordType, so I choose sqlite.BLOB type for it.

@kvesteri All tests are green now.

[kvesteri]

Thanks for the PR! 🚋