[api] relax android device id check

Android official document says the device id should be 16 chars in hex repr,
but some users report that their device ids is only 14 or 15 chars long.
So we accept any device id with a length of (0,16].
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[repo create] enable cache for loading 'repo_crypto.js'
highlight keywords in 'search result' and 'file view' page; bug fix for pdf view
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Fix user traffic checking bug when record is empty
Merge branch '3.0'
Remove unused imports
Fix unable to log bug in seahub/utils