Update Add/Edit time form

[keunes]

• Update some labels
  
  In the add/editing mode, the first option has the label 'Name', where this data is displayed as 'Details' everywhere else (e.g. index table). Others: Open tasks -> Task (it is already clear from the list that only open tasks can be assigned).
• Reorganise field order (to reflect logic and index table)
  
  Proposal:
  • Date
  • Assign to [index table: Name]
  • Open tasks Task
  • Name Details
  • Description Additional info
  • Hours
  • Billable
  • Private [not in the index table]