Update adblockplusui dependency to 7b76422235a0 (release-2019-4)

Background

This imports the following changes: https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/compare/release-2019-3.2...release-2019-4

See also Release 2019-4.

What to change

• Change adblockplusui dependency to hg:7b76422235a0 git:697149d.
• For https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/812:
  • Drop support for Opera 39 (see #185 (closed)) or fix the regression described in the UI issue.
• For https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/638:
  • Increase block element window size from 420x200 to 600x300.
  • Update block element highlight styles
    • Replace box-shadow: inset 0px 0px 5px {color} with border: 2px solid {color}.
    • Replace highlight colors with #CA0000
  • Update "composer.dialog.init" message: Add "highlights" property to indicate number of highlighted elements.
• For https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/761 and https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/807:
  • Add "composer.content.preview" message to toggle element blocking preview.
    • Support "active" boolean property to indicate whether to activate or deactivate preview.
  • Disable preview when being done with block element feature.
• Update metadata.base:
  • Import the following files:
    • adblockplusui/skin/icons/cancel.svg (see https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/472)
    • adblockplusui/skin/icons/share-on-weibo.svg (see https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/642)
    • adblockplusui/skin/icons/updates/block-element.gif (see https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/704)
  • Stop importing the following files:
    • adblockplusui/skin/icons/weibo.svg (see https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/670)
    • adblockplusui/skin/icons/star.svg (see https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/706 and https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/769)
    • adblockplusui/skin/icons/web/navbar-logo.svg (see https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/818)

Hints for testers

See hints for testers in individual issues.