Don't use ::TerminateThread()

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
Make it possible to abort loading branches/tags thread

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
Check if window is exist in working thread

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
CChooseVersion::InitChooseVersion() supports to no block OK button

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
Show "Loading" while loading branches/tags

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>