Adapt to changes in Gerrit core

Update the UI components to align with recent core changes and remove
deprecated Polymer elements. Core migrated to Material components
and moved away from legacy 'paper-*' and 'iron-*' elements. Explicit
'on-input'/'on-change' handlers replace the two-way 'bind-value usage.

Change-Id: Ife216d056b00748bdf2e3c31d4fe0ac2d4ab8f69