Bypass usage of LDAP when getting number of Codenvy on-prem users in Installation Manager

[dmytro-ndp]

There is a method com.codenvy.im.managers.LdapManager#getNumberOfUsers in Installation Manager which is used:

1. by com.codenvy.im.service.LicenseService#isCodenvyUsageLegal to verify if Codenvy is being used legally according to Codenvy license;
2. by com.codenvy.im.service.ReportSender#sendNumberOfUsers to send report with number of users to the data@codenvy.com ones a week on Sunday morning.

Fix stages:

• move Codenvy License management staff to Codenvy API Server [Move Codenvy License management staff to Codenvy API Server #599]
• move User Number Report Sender to Codenvy API Server [Move 'User Number Report' sender to Codenvy API Server #600]

This issue depends on #597.