[ui] Job design form enhancement

Some enhancement ideas for the job design form:

1. Currently, the file chooser pops up when people click into the "jar path", "files", or "archives" inputs. This can be annoying sometimes, because the file chooser makes you choose starting at the filesystem root. And perhaps HDFS is slow and I just want to type in the path. Maybe we can have a button (the "folder", i.e. file-pick, icon) next to the text inputs. Clicking on the button will pop up the file chooser. But otherwise people can type in the text input freely.
2. The job properties sometimes are HDFS paths. We can similarly place a button next to the value inputs, to help users with picking a file.
3. The files and archives text inputs could be longer. (Those fields are always HDFS paths.)