filter: Fixes setting sample delay declaration for the PFB channelizer and in GRC.

Addresses issue #695.
filter: Fixes setting sample delay declaration for PFB synthesizer in GRC.

Addresses issue #695.
runtime: fix installation location of the gr_log_default.conf log configuration file.

Addresses issue #720.
cmake: Additional search path for QWT include files.

This is specific to QWT5. In 3.8, we will likely move to QWT6.

Addresses Issue #735.
audio: Fixes string format bug in ALSA error messages.

Addresses issue #736.
Merge branch 'maint'