Refactor New Portfolio page according to designs.

New designs call for a streamlined New Portfolio page, with far
fewer input options. This commit refactors that page according to those
designs.

Some of the route functions in this commit refer to a "step 1" of creating
a new Portfolio. Though there is no "step 2" right now, the designs call
for a multistep flow for Portfolio creation process, so this commit sets
the stage for that.

atst/models/portfolio.py

@@ -1,6 +1,5 @@
 from sqlalchemy import Column, String
 from sqlalchemy.orm import relationship
-from sqlalchemy.types import ARRAY
 from itertools import chain
 
 from atst.models.base import Base
@@ -19,19 +18,11 @@ class Portfolio(
 
     id = types.Id()
     name = Column(String, nullable=False)
+    description = Column(String)
     defense_component = Column(
         String, nullable=False
     )  # Department of Defense Component
 
-    app_migration = Column(String)  # App Migration
-    complexity = Column(ARRAY(String))  # Application Complexity
-    complexity_other = Column(String)
-    description = Column(String)
-    dev_team = Column(ARRAY(String))  # Development Team
-    dev_team_other = Column(String)
-    native_apps = Column(String)  # Native Apps
-    team_experience = Column(String)  # Team Experience
-
     applications = relationship(
         "Application",
         back_populates="portfolio",