Move capture start button to the toolbar

Move the capture button from the bottom to the toolbar. This makes it visible
even if parts of the window are hidden.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Remove toplevel windows from plugin glade files

There is no need to have a toplevel window for the plugin glade files. Removing
them saves us from having to unparent the panel first.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Add support for device and channel selection

With this patch we can select which IIO device we want to sample from and also
which channels we want to sample.  There are still a few minor issues which need
to be fixed, but more or less it is working.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Move dialog function to its own file

The main osc.c file is getting pretty crowded. Factor out the dialog handling
into its own file.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
fru.c: Fix compile warning

Use %zi instead of %i to format the size_t typed variable.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>