Make sloccount and understand analysis optional

Since understand is a proprietary tool, not every codeface
user will have it installed. Allow for making the respective
analysis pass optional. For reasons of symmetry, also make
sloccount optional, but default to doing the pass.

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
Add sloccount to the list of dependencies

Complexity analysis requires the free software package sloccount.
Add it to the list of required programs in the installation
instructions.

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
Document that stable node.js releases are supposed to be used

The current development version (0.11.x) has problems
with npm package downloads and should be avoided. Document
this explicitly.

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
Add package png to the list of R dependencies

It is required for the shiny server code.

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
Document web server setup

Document all required steps to set up the shiny server
infrastructure that provides the web frontend.

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>