ols: Support get/set/list on all device options

Where it makes sense: _LOGIC_ANALYZER and _TRIGGER_TYPE don't have much
use for all of them.
ignore test leftovers
rigol-ds1xx2: fix handling of partial frames.
rigol-ds1xx2: doesn't actually support SR_CONF_LIMIT_SAMPLES
rigol-ds1xx2: support digital channels.
zeroplus-logic-cube: add USB ID for LAP-16128U
alsa: Set the probe index
demo: Fixed glitching in increment signal
demo: Only one GIOChannel is needed
demo: Keep a pointer to dev_context in sr_dev_inst and vice-versa
session: Make sr_session_stop thread-safe

With the sigrok session running in a worker thread, if sr_session_stop is called
from another thread, it shuts down the pollfds used by the hardware drivers,
without ensuring that the sigrok event loop is no longer using those pollfds.

On the demo driver, this involves shutting down the GIOChannels, causing a
segfault when the sigrok event loop tries to use them. This is evident when
using the Stop button in PulseView, while the session is running.

This isn't a problem with just the demo driver; any driver's resources may be
freed by sr_session_stop concurrently with the sigrok session running.

To solve this problem, we don't touch the session itself in sr_session_stop().
Instead, we mark it for decommissioning and return. The session polls this flag,
and shuts itself down when requested.

This fixes bug 4.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
demo: Moved demo configuration variables into dev_context
demo: Free dev_contexts
demo: Unref the IO channel when it is no longer used
lascar-el-usb: Use two probes for temp/humidity loggers
demo: Fix compiler warning, cosmetics.
Add SWIG interface file and build script for Python bindings.