Fix jquery selector for detecting the pass number field

There was a missing # in the selector. However, since the result was
checked for !== null (and jquery returns an empty array-like object when
nothing matches), this didn't actually prevent the dialog from being
shown).
Don't check jquery result against null

When nothing matches, jquery returns an empty array-like object, not
null. This caused the account selection box to be displayed on all pages
with matching urls, even when there is no actual account number field
(e.g. on the send transactions page).
Remove unused variable
Modify the "value" property, not attribute of input fields

The "value" attribute is the attribute in the DOM / from the HTML, which
sets the initial value of an input field. When the field was
not modified yet, it also sets the current value, but when the field was
modified, changing the "value" attribute not longer has any effect.

The current value of a field is stored in its "value" property (as
opposed to attribute), so modify that one instead.
Support Rabo Scanner login page

This should support the Rabo Scanner login page. Only marginally tested,
I do not have the Scanner yet.
Fix typo in the changelog date
Bump the version to 2.1.0 and update changelog