This PR switches RAWeb from hash-based (e.g. #favorites, #settings) to path-based (/favorites, /settings) routing and URLs. This is possible because we now use vue-router to handle the routing (it was already bundled, but it was unused) and we serve index.html instead of a 404 page.

• IncterceptHtml.cs now (1) serves a static file if it exists, (2) quits early if it detects a path to the API so that the API is not affected, (3) attempts to serve an HTML file with token replacement if it exists, and (4) serves index.html with token replacement if conditions 1-3 were not met. In effect, it replaces non-API 404 pages with index.html. This is common for a single-page app (SPA) like ours.
• HTML token replacement now includes replacing "%raweb.basetag%" with <base href=\"" + VirtualPathUtility.ToAbsolute("~/") + "\" />, so that paths consistently resolve relative to the path to which RAWeb is installed. This is needed when subpaths may be served index.html.
• There is now a 404 page on the web app since the web app now receives all URLs that would have been 404 errors on the app.

The <base> tag is supported by all major browsers: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/base

Tested on Chrome, Firefox, and Safari.