Add GROUP section to Orion events

[alifbe]

Extend Orion event format to support GROUP section alongside the existing WELL section.

Today, group-related events are defined in the SCHEDULE section with group name specified in GROUP attribute. Supporting group section will make these events clearer to inspect and easier to maintain.

Example:

Current setup

SCHEDULE
  @2020-07-01  GEFAC  GROUP=OP  FACTOR=1.0  TRANSFER=YES
  @2020-07-01  GCONPROD  GROUP=OP  CMODE=LRAT  LRAT=20000  WRAT=20000  ORAT=20000  BHP=1*
  @2020-07-01  GCONINJE  GROUP=WI  TYPE=WATER  CMODE=RATE  RATE=16000  BHP=500

Proposed

GROUP "OP"
  @2020-07-01  GEFAC  FACTOR=1.0  TRANSFER=YES
  @2020-07-01  GCONPROD  CMODE=LRAT  LRAT=20000  WRAT=20000  ORAT=20000  BHP=1*

GROUP "WI"
  @2020-07-01  GCONINJE  TYPE=WATER  CMODE=RATE  RATE=16000  BHP=500