container: bring back support for lxc 2.x under a feature flag

Fix media codecs 

(frameworks/av commit c83d228e85b187e3112f10003282c8270d18ef71 moved this
 from media_codecs_google_video.xml to new file media_codecs_google_tv.xml
 for reasons not given.)

Added missing media_codecs_google_*.xml from frameworks/av libstagefright (tree 6b14452cfef637b9b987c0a6a690bda7067afe49).

Upstream location is https://android.googlesource.com/platform/frameworks/av/+/master/media/libstagefright/data

cmds: implement CPU feature sanity check via builtin compiler functions

To prevent our whilelist from growing much more we know do an additional
sanity check via compiler builtin functions if we cannot detect all
mandatory CPU features via the cpu_features libray and if the CPU isn't
whitelisted. This should cover more or less all remaining cases unless
the compiler is unable to detect the features properly.

Update check_features.cpp - Added override for Core i7-720QM

Add option to disable sdl window hit test with envar value

Update check_features.cpp - Added override for Intel Xeon E5520

I also get the same SSE error on a virtual machine with an Intel Xeon Processor:
The CPU of your computer (Intel(R) Xeon(R) CPU E5520 @ 2.27GHz) does not support all
features Anbox requires.
It is missing support for the following features: SSE 4.1, SSE 4.2, SSSE 3

but checking /proc/cpuinfo reveals that it supports the features:
...
model name	: Intel(R) Xeon(R) CPU E5520 @ 2.27GHz
...
flags	: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx rdtscp lm constant_tsc rep_good nopl xtopology nonstop_tsc cpuid pni ssse3 sse4_1 sse4_2 x2apic hypervisor lahf_lm pti

I hope adding the following code into the array in check_features.cpp could fix the problem:
// Intel Xeon Processor E5520
"E5520"

Update check_features.cpp - Added override for Pentium T4500

Add probot stale configuration

We want to get issues without activity closed after a while unless they
are marked with specific labels to keep things clean and maintainable.

Fix clang build errors

cmds: add override for Intel Core i5 M 460

This commit uses GCC friendly pragmas to demote a clang error on
C99-specific feature usage to a warning.

The C99 feature that is used here is compound literals. It gets used
trough a macro from the dbus C library.

This removes the constexpr const char * default_glesv1_lib and promote
-Wunused-const-variable back to error level on clang.

Remove a unused lambda capture on [this] in
anbox::cmds::CheckFeatures::CheckFeatures() and promote
-Wunused-lambda-capture back to error level on clang.

This commit removes the private unused field type_ from anbox::dbus::Bus
and promotes -Wunused-private-field back to error level on clang.

cmds: add override for Intel Celeron N2840