When evaluating a context, we need to use the server format for dates,
because the context will ultimately be sent do the server. Also, moment
objects are not known by pyeval, so they simply cause a crash (for
example, see bank statements form view, edit it, click on 'add an item')
With this commit, we make sure that the evaluation context is correct,
with respect to dates (we use the toJSON method, because that is the way
we get the server compatible date)
Géry Debongnie
1561165fe2