Improve support for user-defined tools

With #309 in progress, we need to implement a way to allow users to specify their own tools.

Suggested approach:
1. TBH, the fine-grained tool categories (fcm ,git, subversion etc each being their own cateforie) would appear a probably useless overkill. Instead, add all these tools as MISC.
2. Allow more than one MISC tool in the tool box.

With this implement, a user can add arbitrary tools (all as `MISC`). This works fine as long as the name of the tools are unique (i.e. we get the tool `svn` or `subversion` from the `MISC` category).

Start by reviewing issue #309, then locate the tool-category and tool-box handling described in this issue. The work is done when users can add multiple uniquely named tools under MISC and retrieve tools such as svn or subversion without introducing separate fine-grained categories.

Written by the indexing model from the issue text.