Proper formatting of BlockClock's remaining sync time

[jarolrod]

Applies proper formatting to the value obtained from nodeModel.remainingSyncTime, as specified in our design docs.

Displays the largest unit of time left until we get to less than 5 hours left, in which case it will shows both hours and minutes. When it reaches minutes, it only shows minutes until there is less than 5 minutes, which then it will display both minutes and seconds.

This works for now, but we'll probably want a different approach so that the units and the word "left" can be translated.

weeks	days	hours	h & m	minutes	m & s	seconds

Fixes #225

[johnny9]

concept ACK

[johnny9]

if you wrap subText with qsTr() it should still be translatable with an appropriate parameterized translation. I just think the static analysis tool won't automatically find the string to translate.

[jarolrod]

@johnny9 I think that we should wait until we have translation wiring setup so we can test with Qt what will work in terms of recognizing strings to translate

[johnny9]

ACK 542e4d4