fixes #173:

• adding an extension setting for normalizing tags (disabled by default)
• when enabled, changing the Tags input label to Tags [normalized] (for clarity)
• when enabled, applying tag handling logic from buku on tag addition/removal (this also covers input validation)

also:

• preserving whitespace when rendering tags
• removing webext archive before making a new one (otherwise it gets bloated on multiple runs due to including all previous page script versions)
• allowing to run make via yarn, i.e. yarn make webext (this works from any subfolder without having to navigate into the project root)