Enhance file upload preview

[GoFroggyRun]

This PR closes #500. A filter, nbsp, is added to disable stripping white spaces. Also modified title name as suggested in #500 by @MattHJensen.

Before this PR, the file upload section looks like:

The new file preview looks like:

where the uploaded file looks like:

{
    "policy": {
        "_SS_Earnings_c": {"2018": [400000], "2019": [500000], "2020": [600000], "2021": [600000], "2022": [600000], "2023": [600000], "2024": [600000]},
        "_II_em": {"2018": [8000]},
        "_II_em_cpi": {"2018": false,
                       "2020": true},
        "_ALD_InvInc_ec_rt": {"2019": [0.20]}
    }
}

[martinholmer]

@GoFroggyRun, Thanks for the fixes in pull request #701.

[hdoupe]

@GoFroggyRun this looks good, are you ready for this to be merged?

[GoFroggyRun]

@hdoupe Yep.