Add viewdata::marked variable

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Add linemarked.ico

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
TortoiseGitMerge: Mark block

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
TortoiseGitMerge: Use left file except marked blocks

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>