move alloc spatial picture and free spatial picture to CWelsPreProcess
add update spatial pictures method too CWeslPreProcess
move spatial picture related variable to CWelsPreProcess
correct code style
update to the last commit: interface change
Merge branch 'master' of https://github.com/cisco/openh264 into develop_b
correct style
Merge pull request #290 from volvet/develop_b

Refactor CWelsPreProcess