[Android] support preinit && predonload mode (#2491)

# feature : 
1. supprot preDownLoad bundle
2. support preInitInstanceContext

# performance : 
1. 200ms improve 

# usage: 
add url  params 
- ` ?preDownLoad=true`
- or `?preInitInstance=vue/rax`
- or both of them `?preDownLoad=true&preInitInstance=vue/rax`

# sample: 
- case: `http://editor.weex.io/compiled/8afdb78575e9cbbdf35d32d102843885/bundle.weex.js?preInitInstance=vue&preDownLoad=true`
- originurl: `http://editor.weex.io/compiled/8afdb78575e9cbbdf35d32d102843885/bundle.weex.js`

3 files changed
tree: 9cf0c1f0aaa4463bb51d048e312a50a4fd9ff106
  1. src/
  2. tools/
  3. build.gradle
  4. proguard-rules.pro