SQL Explorer 0.2.0

Show the interface in the README with sample data

The README described the application in words alone. A reader could not see
the window, the tree, the editor, the result grid or any dialog before a
build.

The README now holds twelve pictures of the interface under a Screenshots
section, in the groups of the connections, the objects and the statements.
Each picture carries a short text that says what it shows. The pictures come
from the interface with sample connections and sample rows, so they hold no
real server, no real user and no real row. They stand in docs/screenshots/.