Progress details for publish api

[sliverc]

This introduces progress detail for publish api based on non locking and async api in PR #459. Hence PR #459 needs to be merged first before merging this PR.

Relevant changes in this PR are commits smira@005ce6f and smira@27aa816

Example:
GET /api/tasks/TASK_ID/detail (replace TASK_ID with publish task)

Result would look like this:

{
  'RemainingNumberOfPackages': 102,
  'TotalNumberOfPackages': 546
}

Checklist

• unit-test added (if change is algorithm)
• functional test added/updated (if change is functional)
• man page updated (if applicable)
• bash completion updated (if applicable)
• documentation updated
• author name in AUTHORS

[codecov]

Codecov Report

Merging #675 into master will increase coverage by 0.21%.
The diff coverage is 61.59%.

@@            Coverage Diff             @@
##           master     #675      +/-   ##
==========================================
+ Coverage   60.64%   60.86%   +0.21%     
==========================================
  Files          50       54       +4     
  Lines        6276     6436     +160     
==========================================
+ Hits         3806     3917     +111     
- Misses       2033     2093      +60     
+ Partials      437      426      -11

Impacted Files	Coverage Δ
deb/changes.go	59.91% <ø> (+0.17%)	⬆️
deb/index_files.go	42.67% <0%> (ø)	⬆️
deb/list.go	79.55% <0%> (ø)	⬆️
files/package_pool.go	67.17% <0%> (ø)	⬆️
context/context.go	11.72% <0%> (-0.4%)	⬇️
deb/package_collection.go	54.83% <100%> (+3.32%)	⬆️
deb/local.go	92.78% <100%> (+5.65%)	⬆️
task/task.go	100% <100%> (ø)
database/leveldb.go	79.24% <100%> (-2.12%)	⬇️
http/temp.go	77.77% <100%> (ø)	⬆️
... and 11 more

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