Autocompletion for metrics in Aim UI

[jgiannuzzi]

• When typing run. in the various explorers, metrics should be available as a suggestion.
• After having typed run.metrics in the various explorers, a list of valid metric names should be suggested (e.g. ["loss"], ["wps"], etc. — they should come from the project's metrics list (GetProjectParams)).
• After having type run.metrics["metric-name"], .last should be suggested
• when typing metric. in the metrics explorer, the following attributes should be suggested: name and last