Backendlib should provide installed_time, installed_size, app_size, data_size

BUG=XWALK-2459

backendlib should set those field in pkgmgr detail info structure.

pkgcmd -s -t wgt -q -n ${pkgId} # should return this data

|----------------------|---------------|---------------|-------------|-------------|
| field                | installed WGT | installed XPK | package WGT | package XPK |
|----------------------|---------------|---------------|-------------|-------------|
| installed_time       | YES           | YES           | N/A * 3)    | N/A * 3)    |
|----------------------|---------------|---------------|-------------|-------------|
| installed_size       | YES           | YES           | N/A * 4)    | N/A * 4)    |
|----------------------|---------------|---------------|-------------|-------------|
| app_size             | YES           | YES           | N/A * 4)    | N/A * 4)    |
|----------------------|---------------|---------------|-------------|-------------|
| data_size            | YES * 2)      | YES * 2)      | N/A         | N/A         |
|----------------------|---------------|---------------|-------------|-------------|
| min_platform_version | YES           | NO * 1)       | YES         | NO * 1)     |
|----------------------|---------------|---------------|-------------|-------------|

 1) No field in manifest.json, will be empty
 2) Based on size of 'tmp' and 'private' directories of widget
 3) Will return 0
 4) Will return 0, this field was not set for tizen 2.x either

This information may be present in other apps to user if he/she want to install app.
Merge pull request #2414 from tiwanek/XWALK-2459

Backendlib should provide installed_time, installed_size, app_size, data_size