Make component classes final

[wraitii]

Rationale: read ​this and this ​this. Basically: our component classes cannot be inherited from (they are final). We should show this semantically. I'm not actually sure it'd help with devirtualization, but it probably can't hurt.

So we should add "final" to our C++ components.

If you feel very strongly against this, please speak now or forever hold your tongue.

[Vladislav Belov]

Is it supported by GCC 4.6 and VS2013? Also it'd good to have override and default/delete instead of = 0;.

[Stan]

Visual studio doesn't support it see ​https://blogs.msdn.microsoft.com/vcblog/2013/12/02/c1114-core-language-features-in-vs-2013-and-the-nov-2013-ctp/

Attributes line

Same for 2015 ​https://blogs.msdn.microsoft.com/vcblog/2014/11/17/c111417-features-in-vs-2015-preview/

[echotangoecho]

IMO, we can increase the minimal requirement for the GCC version to GCC 4.8 without affecting much (if any) users, (Ubuntu 12 LTS, which has GCC 4.6 as latest GCC version, has a lifetime ending in a few months). For visual studio, final is supported starting from MSVC 11 (​http://en.cppreference.com/w/cpp/compiler_support).

EDIT: Additional note: default/delete is already supported from all compilers we minimally require currently, as can be seen from the link I posted.

[elexis]

Backlogging due to lack of progress

[Imarok]

Move tickets to their correct component.