Issue #276: Enable to bulk clear ignore area for test runs list and details view.

[suratdas]

Addresses issue Visual-Regression-Tracker/Visual-Regression-Tracker#276
Changes included:

1. Clear icon will clear ignore area of the selected images.
2. Apply ignore area icon will be enabled only one selection and then on confirming apply, it will apply the selected ignore area to all images in the build.
3. For small number of selection, both the "wait for processing" snackbar and success snackbar come almost at the same time which may confuse users. Replace this with a progress bar under the action icons.

I will raise a matching backend pull request if this is approved in principal. Here are some screenshots for reference.

[pashidlos]

I like part with clear ignore areas
would you like to add the same button in test run details modal to clear ignore areas for specific test run?

the part regarding copying is not quite clear for me
not sure that this would be useful if it's not possible to select target test runs

[suratdas]

Removed apply logic now. Will implement later from details view.

[pashidlos]

LGTM