Docsite: watch issues

[miroslavstastny]

gulp watch does not pick changes on Windows

1. On Windows, run yarn start
2. Edit component source
3. build:docs:docgen should be triggered, but nothing happens

The reason is that the watch path contains backslashes as path.resolve(), which is used to construct it, uses backslashes on Windows.
According to documentation glob pattern must contain forward slashes only.

Incremental build breaks examples menu

For each component single JSON file with a list of examples is built from multiple index.tsx files.
When one of the files is changed, watch triggers incremental build for the single changed file, and the resulting JSON is overwritten with data from that single file only.
(Have types and variants examples, update types' index, all variants are now missing in example menu).
This can be solved by adding gulp-remember to the watch pipe.