issue0008: less update message

1. reduce update progress message
2. use taskqueue chan to start downloaderw

Change-Id: I6c9789397dca0c8ee15d52e7112d0a8b69f336bf
issue0009: quick download

if file & md5 exist, verify md5 first

Change-Id: I20ffacf155274406d586fe15bf318fb4d270a0b9
issue0010: Wait signal

Change-Id: Ib71b04dfbfb78396b29759b905fc6f30b0a18bb1
issue0011: Fix muti download progress struck

if a task with empty urls list, it will struck. so cancel and send Stop && Error signal when it start

Change-Id: I2a7184ccab93cb0cc98e16e3dff3f5730417ab12
issue0012: add ftp soupport

Change-Id: Ifefe0f25ee80fe3b64fecf550d301342b866414a
issue0013: fix path structure

Change-Id: I5aa31daec7f990931c7c7ec7cc0b4b57b5ea9d3a
issue0014: Replace int32 ID with uuid

Change-Id: I10f1a75eed6f75d47702f1a3c4e5c8a6333eedcc
issue0015: ftp support rest range

Change-Id: I00bcc806c9fe0ef4d880370f23622ff6162dd65d
issue0016: fix download error with big file

if the server do not support range/rest, when download a big file, the memory alloc onec time, that will case failed,
so write when cache failed

Change-Id: Id82956ed1810556917194bcedf79c089dd9a8dbf