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[mattesmohr]

This merge fixes the environment, adds new symbols and uses form validation.

Environment

The environment for HTMLKit will be now stored in the application storage of Vapor. This way, the environment stays cached.

Symbols

Symbol(system: "chart.pie")
Symbol(system: "clock")
Symbol(system: "envelope")
Symbol(system: "file")
Symbol(system: "folder")
Symbol(system: "house")
Symbol(system: "lock")
Symbol(system: "person")
Symbol(system: "photo")
Symbol(system: "text.aligncenter")
Symbol(system: "text.alignjustify")
Symbol(system: "text.alignleft")
Symbol(system: "text.alignright")

Form validation

Form(method: .post) {
   FieldLabel(for: "email") {
      "Email"
   }
   TextField(name: "email")
}
.onSubmit(perform: .validate("form", [Validator(field: "email"], rule: .value)])