This includes explanation and context for non-obvious cases and
shortens debug cycles when just-in-time debugging is not available
(like on Linux) by immediately printing description of the assert
as well as symbolized backtrace.
This helps to ensure that a base class that changes underneath us
would not leave any overridden functions hanging.
This already highlighted some questionable use of GTKMM's API,
which were also fixed in this commit.
This is good practice and helps to catch bugs. Several changes
were made to accomodate the newly enabled warnings:
* -Wunused-function:
* in exposed/, static functions that were supposed to be inlined
were explicitly marked as inline;
* some actually unused functions were removed;
* -Wsign-compare: explicit conversions were added, and in
the future we should find a nicer way than aux* fields;
* -Wmissing-field-initializers: added initializers;
* -Wreorder: reordered properly;
* -Wunused-but-set-variable: remove variable.
-Wunused-parameter was turned off as enabling it would result in
massive amount of churn in UI code. Despite that, we should enable
it at some point as it has a fairly high SNR otherwise.