[stats] introduce stats module (WIP)

Still need to:
- collect requests stats
- save stats over multiple run
- guess data access info
- send stats to stats.restx.io
[stats] collect requests stats

Still need to:
- save stats over multiple run
- send stats to stats.restx.io
- guess data access info
[stats] implement stats storage

Still need to:
- send stats to stats.restx.io
- guess data access info
[stats] add javadoc and refactor some details

for clarity and performance
[minor] fix page title
[minor] put stats resource in restx-admin group
[minor] don't use Long.MAX_VALUE for minDuration default value

it's causing problems with jackson deserialization
[stats] file storage period is 5 minutes by default
[stats] implement stats sharing
[stats] add log and link to page documenting stats
Merge pull request #105 from restx/stats

[stats] introduce stats module