global: PostgreSQL Text type compatibility fix
global: PostgreSQL Text type compatibility fix

* BETTER Improves compatibility of Text fields in PostrgeSQL by
  changing Text in models and removes Invenio hacks on MySQL Index and
  Primary Key creation because starting from SQLAlchemy>=1.0 it arises
  an exception if the length is specified. (addresses #3037)

* Updates minimum Flask-Admin version to 1.1.0.

* PEP8/257 code style improvements.

Signed-off-by: Leonardo Rossi <5460ec99b71a72e7693c4088b5c2585e76e1c857@cern.ch>

inspirehep/invenio-accounts,inveniosoftware/invenio-accounts,tiborsimko/invenio-accounts,inspirehep/invenio-accounts,tiborsimko/invenio-accounts,inspirehep/invenio-accounts,tiborsimko/invenio-accounts,inveniosoftware/invenio-accounts,inveniosoftware/invenio-accounts