Tools should be extracted to plugins

[janisozaur]

A tool should be defined as a plugin. Qt has nifty plugin system based on QPlugin and QLibrary. Carto should use former to load its tools on init.

[janisozaur (janisozaur)]

revid:janisozaur@elektrybalt-20100711010012-z97tgx3njk9oe9i6 in lp:cybercarto solves this problem by extracting the only tool in existence, pencil, into statically linked plugin. you'll need branch lp:~carto-team/cybercarto/plugins at the same level as cybercarto to successfully compile.
external plugins should be loaded as dynamic plugins.