Better YAML overriding

Now it does not take just the root element into the account, but it crawls throught the dictionary and only updates the values that are present in the new dictionary. It converts all dicts to Configs, other values than specified in override dict are not touched.
My counterproposal...
Added new Tree element
Re-vamp of Development Guide
infra_providers: Refresh

* Added possibility to refresh the query to speed things up
* Made the check for settings use the refresh if the data have not come yet
Cleanup and slight additions to docs
vms_subpages/details.py: wait_for
pages/cloud/instances/__init__.py wait_for
Merge pull request #300 from mfalesni/provider_refresh

Provider refresh + wait_fors
Merge pull request #299 from psav/docs_update

Docs update
Merge pull request #290 from psav/tree_element

Added new Tree element
Merge pull request #296 from seandst/recursive-update-yaml-load

Recursive update yaml load
Added InfoBlock
Merge pull request #298 from psav/infoblocks_element

Infoblocks element