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 <leonardo.r@cern.ch>