Installer Jobs list clean up

Installer Jobs list clean up

[Issue#] N/A
[Problem] wrt-installer cannot be used to install/uninstall
    multiple widgets at once. Because of that,
    InstallerLogic does not need to use the Jobs container
    for the jobs.
    InstallerLogic can run/use just one job at given time.
[Cause] N/A
[Solution] container is exchanged for a single pointer
    value that holds the job.
[Verification]  Verification should contain:
    running wrt-installer -p (plugins installation)
    installing, deinstalling, update widgets
    installing invalid widget (that should
    not be installed)

Change-Id: Ib738f61551c5fb39085b6c972b152c9515c9711f