Always clear selection after visual command.

If you keep the '< and '> mark in the command line window, the command
will be treated like an Ex-range command, in which case the Ex-parser
will set and clear a selection for that range.

If the command line doesn't contain an ex-range, Vrapper needs to make
sure the selection gets cleared after executing the command, otherwise
we go back to normal mode with a selection active.

Fixes #554.
Fix string-split expression for Java 8.

Java 7 and older String.split(..) methods put an empty at the start of
the resulting array when splitting using the empty string. Java 8
actually changed this to leave out this empty string, causing an off-by-
one error.

Split using a zero-width expression instead which should behave the same
on any Java version from 5 to 8.

Fixes #565.