[RFC - please comment] track stable branches instead of hashes.

[RFC - please comment]  track stable branches instead of hashes.

v2: (Tadao Tanikawa)
The revision of meta-qt5 is 'master' (not 'dizzy') to keep tracking
latest stable version of Qt5.

v1: (Jan-Simon Möller)
We want the stable branch, but do we really want to maintain the exact commit?
Tracking the stable branches is easier and we inherit the fixes w/o changing our manifest again.

Please comment. If this is fine please merge.

Especially this should be changed:
<project name="meta-openembedded" path="meta-openembedded" remote="openembedded" revision="9efaed99125b1c4324663d9a1b2d3319c74e7278" />

otherwise we are  "147 files changed, 7967 insertions(+), 888 deletions(-)"
behind dizzy branch for meta-openembedded !
Multiple CVEs were fixed in the branch already.

Change-Id: I31689d8ea49d8c876be8bb5608df89ad4c459ab9
Signed-off-by: Jan-Simon Möller <jsmoeller@linuxfoundation.org>
Signed-off-by: Tadao Tnikawa <tanikawa.tadao@jp.panasonic.com>