Feature request: Create and apply design guideline more consistently

[akphi]

• For context menu and dropdown, use Title Case
• Check all placeholder text -> remove ... in placeholder=, use either form: field purpose (in form and limitted space) User Name or long instruction e.g. org.finos.legend.* or Enter a string to do something
• Update button title= to use Sentence case:
  • non-blocking dialogs: some actions, e.g. Choose a source, etc.
  • other types of dialogs: some titles: e.g. Execution Plan, Query Builder, etc.

• Update dialog titles: search for modal__title
• Whenever we have a button that might trigger a modal -> add ... to the tooltip/label (this is UX convention to prompt further actions)
• IMP update design guide to follow this more strictly