INBUXA's name and site where the webmail still said ihasmail

- The sign-in footer names the build "INBUXA webmail" and links to
  inbuxa.org, next to its AGPL source link.
- About gives the INBUXA webmail version, and credits ihasmail on a line
  of its own.
- The user menu's "About ihasmail" is "About INBUXA", to inbuxa.org. The
  Documentation entry pointed at ihasmail's docs; it's gone until INBUXA
  has documentation of its own.
- The startup log says "mail server:" rather than naming the server
  software.

"About INBUXA" and "Built on {ihasmail}" are translated in all nine
catalogues.

web/src/locales/nl.ts

@@ -827,6 +827,8 @@ export const catalog: Catalog = {
     "Default mail app": "Standaard e-mailprogramma",
     "Documentation": "Documentatie",
     "About ihasmail": "Over ihasmail",
+    "About INBUXA": "Over INBUXA",
+    "Built on {ihasmail}": "Gebouwd op {ihasmail}",
     "About": "Over",
     "Server": "Server",
     "Server capabilities": "Servermogelijkheden",