More tool panel manager unit tests.
(Including adding file missing with previous commit 697b58f0.)
PEP-8 and style tweaks to tool_panel_manager.py.
Unit test for tool panel merging tools by tool shed lineage.
Add tool lineage test for tools outside of sections.
Introduce new abstraction of tool lineages.

 - Don't force non-toolshed tools into the tool shed install database.
 - Abstract out dealing with the tool shed install database from toolbox, to potentially allow other tool lineages implementations.
Introduce ToolPanel abtraction.

There are some repeated operations on an odict in Toolbox that could be cleaned up (fewer lines of code, more readable) with new abstraction in place. Starting with __add_tool_to_tool_panel but will work its way to other methods in Toolbox eventually.

Abstraction reduces cyclomatic complexity of Toolbox.__add_tool_to_tool_panel from 23 down to 18.
Simplify toolbox.load_tool_tag_set method.

guid is taken as input but is always produced the same way from the same input, so just derive it inside the method instead.
Hide details of toolbox.tools_by_id from lib/tool_shed/util/tool_util.py.
Centralize abstraction for removing tools from toolbox.

Shield's toolbox.tools_by_id from lib/tool_shed/galaxy_install/tools/tool_panel_manager.py.
Abstractions for registering tools from outside toolbox.

Part of effort to further limit exposing tools_by_id directly outside Toolbox.
Introduce abstraction to prevent lib/galaxy/workflow/modules.py from needing tools_by_id.
Eliminate direct in/get checks against toolbox.tools_by_id - use get_tool or has_tool.
Eliminate walking over tools_by_id externally from toolbox.
Move more logic into ToolSectionElements, raising level abstraction in Toolbox.
Replace another repeated idiom in Toolbox with higher level method in toolbox.panel.