Make necessary changes to blocks when changing tabs

[lizlooney]

Since #224 was merged, the blocks are not being loaded each time the users changes tabs.

When an editor becomes the current editor, it needs to go through the blocks in the workspace and call mrcOnLoad on each block that has an mrcOnLoad method.

[alan412]

It might be possible to do this where you only have to update certain types of blocks and perhaps only if the mechanism or robot it depends on has been updated since you last refreshed this module.

[lizlooney]

We only need to call mrcOnLoad on the blocks that has an mrcOnLoad method.