This fixes the bug where clicking on a border would enable border
dragging even if the border was hidden under a view.

Letting wio_view_at() report where the given coordinates are on a view
enables us to check for views and borders of views in the same loop,
easily solving this problem.

Additionally this makes the border dragging code cleaner and enables
other functions as well to see where on a view was clicked.
---
 include/view.h |  11 ++++-
 input.c        | 110 +++++++++++++++++--------------------------------
 view.c         |  48 ++++++++++++++++++++-
 3 files changed, 94 insertions(+), 75 deletions(-)
[message trimmed]

This matches Rios behaviour, with the small exception that wios resizing
is smooth while Rios snaps to a grid.
---
 include/server.h |   4 ++
 input.c          | 163 ++++++++++++++++++++++++++++++++++++++++++++++-
 output.c         |  36 ++++++++++-
 3 files changed, 200 insertions(+), 3 deletions(-)

diff --git a/include/server.h b/include/server.h
index 4e729a1..60842e1 100644
--- a/include/server.h
+++ b/include/server.h
@@ -26,6 +26,10 @@ enum wio_input_state {
 	INPUT_STATE_RESIZE_SELECT,
[message trimmed]