install-chef-suse: Stop removing redhat_install/ubuntu_install

This is not in the crowbar json template anymore, so no need to make
them empty in crowbar.json.
json-edit: Add ability to remove attributes
json-edit: Spacing fixes
json-edit: Fix setting/removing of some non-existing subattributes

If there's already an attribute like foo.bar set to "test", then it was
failing when trying to do something on the foo.bar.foo attribute.

Now, when setting, we overwrite foo.bar to be a hash, and when removing
we just exit early.
[Devguide] Formatting tweaks

* Line wrap at 80 characters
* Remove trailing whitespace
* Properly indent HTML table
* Remove bullet for "Before submitting pull requests...", since
  there's only one item
[Devguide] Add links to the community Ruby and Rails style guides
Merge pull request #1878 from jamestyj/master-style-guide

[Devguide] Add links to community Ruby and Rails style guides
Merge pull request #1875 from vuntz/install-chef-suse-tweak

install-chef-suse: Stop removing redhat_install/ubuntu_install
Merge pull request #1877 from vuntz/json-edit-improvements

Several improvements to json-edit tools (for pebbles, suse-only)
Merge pull request #1876 from vuntz/install-chef-suse-network

install-chef-suse: Use network config from /etc/crowbar/network.json
install-chef-suse: Fix network validation

We shouldn't validate the two json files, just one.