Fix test broken in #4422 by updating the snapshot.

Add container with overflow hidden to prevent scrollbars from playhead

Update l10n

Revert "chore(package): update scratch-l10n to version 3.1.20190123150639"

chore(package): update scratch-l10n to version 3.1.20190123150639

Throttle costume and watermark updates

Update scratch-blocks to the latest version 

Adds unit tests for this HOC.

Use PureComponent instead since it is a simple shouldComponentUpdate check now.

Update scratch-vm to the latest version 

Move the mask on the audio meter outside the SVG for repaint performance

Remove the redux throttle for targets update.

Disable target updates while sound recording

This fixes the root cause of #2858, which is caused because we are rendering the sound editor based on the GUI editing target data, but retrieving the sound based on the vms editing target data. The throttle of the redux action was causing those to get out of sync while a project was running.

The throttle is not needed because the vm runtime already batches those updates at 30 fps. The updates that come from top-level actions like switching sprites go out immediately.

This is also a minor performance boost, because there was a few ms being spent in setting and checking timers that were not needed.

Closes #4408

Improve sound editor performance with longer sounds

chore(package): update scratch-vm to version 0.2.0-prerelease.2019011…

Remove transition on sprite tiles to make placeholder not flash black.

Remove scale transition from green flag, stop and sound editor buttons

chore(package): update scratch-render to version 0.1.0-prerelease.201…

Update WeDo 2.0 extension name

Closes #4378

Forcing the playhead onto its own painting layer removes an expensive composite with the waveform. Animate using transforms instead of left prevents layouts of the rest of the page while playing a sound.

The waveform component was being re-rendered while the playhead changed, which is a costly operation because it has to calculate the full svg path data string.

Also use white as the background since it gives the same impact and will not look bad if the filter isn't applied or takes a while to be applied