1757 fixes

[na9da]

Contains the following fixes to pre-rendering:

• Captures all CSS styling including those generated by styled-components
• Directs requests to /proxyabledomains and /proxy to locally running server.
• Hides errors or other modals from the rendered output.

[soyarsauce]

You have no idea how pleased this makes me @na9da - bloody awesome work on addressing the styling issue in v8 for this.

I've made a small tweak to use webpack, even though it shouldn't be cause for problem (from doing it in TerriaMap), simply to cover https://github.com/TerriaJS/terriajs/blob/8d5ef29c5fa2e758aebad313024d460a34817a68/buildprocess/runWebpack.js#L4-L5. Just as I know this particular config has worked for terrace

[soyarsauce]

Also, while testing it occurred to me that disclaimer is no longer fixed, so I've raised an issue for that here

[soyarsauce]

Will let CI etc checks via target branch 1757-mobx-tm-new-routing