add additive seeking

Add additive seeking:
If useadditivetimeseeking property in advanced settings set to true, then functionality of analogseeking changed to additives seeking:
hitting analogseeking action more that once increases or decreases how far it will seek after a delay (currently 1500ms) using these step sizes 30s -60s - 3m - 5m - 10m - 30m- 1hr-2hr-3hr-etc.

The feature can be enabled in gui settings->playback->Using additive seeking instead of variable speed seeking
The steps and delays can be configurated in video section of advancedsettings.xml:
      additivetimeseekwaitforseekingstart - dealy between  two action,before starting seeking
      additivetimeseekwaitfordisplayhide - delay before hiding of seeking dialog 
      additivetimeseekstepone - seek time after frist hit
      additivetimeseeksteptwo - seek time after second hit
     additivetimeseekstepthree - seek time after third hit
     additivetimeseekstepfour  - seek time after fours hit
     additivetimeseekstepfive- seek time after fives hit
     additivetimeseekstepother- seek time for all other hits.
I prefer braces even with a single line afterwards. I remember a case with missing bracktes then a dev added a line but forgot to add brackets. From a visual perspective the error was hard to spot. So keep it simple and add them always.