Fix the width of select2-container, to fix NextGen compatibility issue

Fixes #416
More specific CSS selector
Fix position of CSS line
Changing width to 350px for mobile compatibility
Merge pull request #417 from x-team/nextgen-compability

Fix the width of select2-container, to fix NextGen compatibility issue
Merge branch 'issue-433' of https://github.com/x-team/wp-stream into issue-433