Graphepg movement algorithm

[SimonCapewell]

More graph EPG fixes:

1. Fix reported crash when not using cached EIT data
2. Removes an unintentional full screen invalidate when navigating within a page of the EPG when service numbers are shown. getTextBoundarySize has a side effect of invalidating the instance it's using to parent a dummy label used to calculate the text size. A better solution would be to expose a C++ method somewhere similar to eLabel::calculateSize, however I've not found any suitable guidance on how to get set up to develop with the e2 c++ code.

There's still a few more improvements to load time that could be made:
Occasional double calls to buildGraphEntry when loading, seems to be after changing channel
Another 100ms can be shaved off the load time of the EPG by caching the graphics. Yes, they're flagged to be cached in the C++ layer, but caching in static variables in EPGList is quicker on repeated opening.