- added injectPlugin method to viewer (see details below)
 * added example plugin
 * allows "plugin" custom elements to add methods to the viewer itself
 * does not allow ovveriding existing methods ! (a bit more secure at least)
 * injection of methods is done by the viewer itself: should allow
for control about what gets injected and what does not
 * this is one (possible) step in the direction of a modular viewer
for some uses (see issue #36)
Merge branch 'modular'