Change clocks to std::chrono

[ksmith0]

Robert reported an issue with the terminal timeout in pacman mode not responding. It was tracked down to the time comparison in CTerminal.cpp

if (currentTime > (commandRequestTime + commandTimeout_)) {
...
}

I suggest we change all clocks to std::chrono to provide more cross system support and unify our timing methods.

[ksmith0]

Support for chrono was added in gcc 4.4 (https://gcc.gnu.org/gcc-4.4/changes.html) which is our minimum version at the moment.

[cthornsb]

Changed to std::chrono::steady_clock in commit d607d0a. I couldn't find any other time variables which were used for anything other than getting the current time and date.

[ksmith0]

We use timers in the statshandler and in poll2 to keep track of the run duration. We should also add a timer to deal with issue #21 (Polling frequency).

Also, we need to abstract the run file class and use that to track run duration etc, but this is a problem for another issue.

[spaulaus]

This, unfortunately, does not work on grpc02. (gcc 4.4.4)

/root/PixieSuite2/Core/source/CTerminal.cpp:42: error: ‘steady_clock’ in namespace ‘std::chrono’ does not name a type

[cthornsb]

Changed std::chrono::steady_clock to ::system_clock in commit c1b297a. The code now compiles on grpc02.

[ksmith0]

@cthornsb Have we changed over all the clocks?