Retrieve informations once and use them in the whole program

• retrieve:
  • ep
  • head block
  • blockchain parameters
  • currency symbol
  • last UD value (only used in money related f())
  • cli_args? (available from the import)
  • configuration (see #79)
  • first block? (used once in issuers)
  • …
• use them in the whole program

This speed-up silkaj execution because requests slow down performances.