Changes use of semicolons

* introduces SEMI lexical production
* all *Semi productions have same name (no distinction between Semi,
  EOL, EOB, ...)
* No extra nodes for optional ";" in expressions (e.g. "if" Expr ";")
Cleans up files

* merges Scala-BasicDeclarations and Scala-Definitions into
  Scala-BasicDeclsDefs (§4 in reference manual)
* Renames Scala-Templates to Scala-ClassesObjects (§5)
* deletes Scala-Imports (are part of §4.7)
* deletes Scala-Paths (are part of §3.1)
* adds references to manual chapters in Scala-BasicDeclsDefs and
  Scala-Types
Cleans up Scala-ClassesObjects