fcl-db: add storage specifiers to some published properties of TField

Please add storage specifier to published properties of TField:

  property LookupCache: Boolean read FLookupCache write FLookupCache **default False**;
  property ReadOnly: Boolean read FReadOnly write SetReadOnly **default False**;
  property Required: Boolean read FRequired write FRequired **default False**;

to does not bloat *.lfm files and reduce their size ...