移动端重建索引应后台运行并可以隐藏进度窗口

[Jonnyan404]

Describe the bug 由于安卓的省电策略， 应用一切换就会导致前台运行终止， 就得从头索引，从而增加key消耗

To Reproduce Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior 能够后台执行索引，完成后给个通知即可。 有错误，就发送错误通知。

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context Add any other context about the problem here.