Change ajax? helper to check only XMLHttpRequest presence

[skojin]

Use ajax? in redirect helper instead of inline check

Fixes #1131

Checklist

• [x ] - An issue already exists detailing the issue/or feature request that this PR fixes
• [ x] - All specs are formatted with crystal tool format spec src
• [ x] - Inline documentation has been added and/or updated
• [ x] - Lucky builds on docker with ./script/setup
• [ x] - All builds and specs pass on docker with ./script/test

[paulcsmith]

Looks great. Thanks @skojin!