mcf: Add support to enable buildhistory

* without creating git repository in BUILDHISTORY_DIR

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>
mcf: Add arguments to enable sstate and default premirror

* change premirror behavior that without explicitly set value
  it won't inherit own-mirrors and set url.
* add --enable-default-premirror to set premirror value with
  yocto mirror
* add shorter --premirror variant for --enable-premirror
* add --sstate-mirror to generate SSTATE_MIRRORS in local.conf
  if you want multiple SSTATE_MIRRORS, repeat that option

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>
mcf: Add support to enable buildhistory repository

* BUILDHISTORY_COMMIT is set to 1 when buildhistory is enabled
* BUILDHISTORY_AUTHOR assignment is generated in local.conf if
  buildhistory author is provided, otherwise it will use author
  from global git config

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>
Update copyright years, small formal changes

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>
gitignore: Split build products section

* remove slash from downloads ignore, so it will also ignore downloads symlink

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>