Fix SQLAlchemy queries for unread submissions
Fix SQLAlchemy queries for unread submissions

This regression was caused by the PEP8 fixes in cd6f4c3, which among
other things changed instances of `x == False` to `x is False`. While
this would not cause a functional change in normal Python, it does cause
a functional change in the context of SQLAlchemy's `filter*`
methods. These methods override `==` but do not appear to override `is`,
so replacing `==` with `is` breaks the query.

I have grep'ed the code and checked the diff of the breaking commit to
make sure this commit fixes all instances of this error.

Fixes #969

harlo/securedrop,jeann2013/securedrop,pwplus/securedrop,micahflee/securedrop,micahflee/securedrop,kelcecil/securedrop,ehartsuyker/securedrop,conorsch/securedrop,jeann2013/securedrop,chadmiller/securedrop,jeann2013/securedrop,jrosco/securedrop,jaseg/securedrop,heartsucker/securedrop,jaseg/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,harlo/securedrop,jeann2013/securedrop,jrosco/securedrop,ageis/securedrop,harlo/securedrop,ageis/securedrop,harlo/securedrop,ehartsuyker/securedrop,jaseg/securedrop,ehartsuyker/securedrop,jaseg/securedrop,kelcecil/securedrop,jrosco/securedrop,jeann2013/securedrop,harlo/securedrop,garrettr/securedrop,kelcecil/securedrop,jaseg/securedrop,kelcecil/securedrop,chadmiller/securedrop,garrettr/securedrop,micahflee/securedrop,conorsch/securedrop,pwplus/securedrop,chadmiller/securedrop,jrosco/securedrop,heartsucker/securedrop,chadmiller/securedrop,kelcecil/securedrop,ageis/securedrop,garrettr/securedrop,heartsucker/securedrop,ageis/securedrop,harlo/securedrop,chadmiller/securedrop,heartsucker/securedrop,jaseg/securedrop,conorsch/securedrop,pwplus/securedrop,jrosco/securedrop,micahflee/securedrop,conorsch/securedrop,pwplus/securedrop,jeann2013/securedrop,conorsch/securedrop,kelcecil/securedrop,pwplus/securedrop,garrettr/securedrop,pwplus/securedrop,chadmiller/securedrop,ehartsuyker/securedrop,jrosco/securedrop,ehartsuyker/securedrop