adding uncertainty to repr for Spectrum1D

[SaOgaz]

If people like this change I can go through all the docs and update any output that needs it.

Here's what it looks like with this change in an ipython session

In [6]: spec = Spectrum1D(spectral_axis=np.linspace(0, 50, 50) * u.AA, 
   ...: ...                   flux=np.random.randn(50) * u.Jy, 
   ...: ...                   uncertainty=StdDevUncertainty(np.random.sample(50), unit='Jy'))                                                          

In [7]: spec                                                                                                                                           
Out[7]: 
<Spectrum1D(flux=<Quantity [-0.79350782, -0.1985586 ,  0.69941613, -1.26048916, -0.30668635,
            0.22692452, -1.48539139,  0.06807652,  2.35720788,  0.08976297,
           -1.34475404, -1.12296945,  0.40057251,  1.34168387, -0.73202276,
           -0.01233865, -0.23764738, -1.18952659,  0.59660562, -2.62269804,
           -0.31162905, -0.29284552,  0.71713381,  0.13721592, -0.03311284,
            0.77818938, -0.09165447, -0.50518192, -1.36158287,  0.4004441 ,
           -1.26370512,  1.36290666,  0.20989722,  0.13344762, -0.43951508,
           -0.11195588,  0.38274015,  0.62751832, -1.4268625 , -2.33907961,
           -0.61735017,  0.16263518, -0.65331399, -0.68958623, -0.93873669,
            0.11189459,  0.1174194 ,  0.96402335,  1.37272333, -0.41412246] Jy>, spectral_axis=<Quantity [ 0.        ,  1.02040816,  2.04081633,  3.06122449,  4.08163265,
            5.10204082,  6.12244898,  7.14285714,  8.16326531,  9.18367347,
           10.20408163, 11.2244898 , 12.24489796, 13.26530612, 14.28571429,
           15.30612245, 16.32653061, 17.34693878, 18.36734694, 19.3877551 ,
           20.40816327, 21.42857143, 22.44897959, 23.46938776, 24.48979592,
           25.51020408, 26.53061224, 27.55102041, 28.57142857, 29.59183673,
           30.6122449 , 31.63265306, 32.65306122, 33.67346939, 34.69387755,
           35.71428571, 36.73469388, 37.75510204, 38.7755102 , 39.79591837,
           40.81632653, 41.83673469, 42.85714286, 43.87755102, 44.89795918,
           45.91836735, 46.93877551, 47.95918367, 48.97959184, 50.        ] Angstrom>, uncertainty=StdDevUncertainty([0.55949932, 0.7743728 , 0.89748501, 0.63007083,
                   0.11617335, 0.11122692, 0.72021224, 0.2168352 ,
                   0.49825998, 0.91373081, 0.1780643 , 0.92995308,
                   0.02226761, 0.73156982, 0.3332609 , 0.03908292,
                   0.96935045, 0.69324456, 0.45283954, 0.01795764,
                   0.3105003 , 0.33231226, 0.40595955, 0.21787728,
                   0.9849537 , 0.7775922 , 0.11466842, 0.14362938,
                   0.63796639, 0.10280555, 0.73154504, 0.57335405,
                   0.73362712, 0.05337787, 0.81576867, 0.66795002,
                   0.75455155, 0.73228133, 0.79322921, 0.25778224,
                   0.58692161, 0.83211342, 0.62523079, 0.57217811,
                   0.43043543, 0.80936413, 0.81700978, 0.63452876,
                   0.25442867, 0.23880276]))>

What it looked like before:

In [30]: new_spec3                                                                                                                                     
Out[30]: 
<Spectrum1D(flux=<Quantity [0.18278657, 0.01050715, 0.27264392, 0.69624523, 1.01334485,
           1.07064075, 0.83599236, 0.43168126, 0.12365467, 0.05162207,
           0.21706343, 0.48931305, 0.62018392, 0.55961905, 0.45844228,
           0.4132248 , 0.45743191, 0.62178518, 0.        ] Jy>, spectral_axis=<Quantity [ 1.5,  2.5,  3.5,  4.5,  5.5,  6.5,  7.5,  8.5,  9.5, 10.5,
           11.5, 12.5, 13.5, 14.5, 15.5, 16.5, 17.5, 18.5, 19.5] nm>)>

closes #470

[nmearl]

This looks fine to me. However, I should note that there ought never be a case where the wcs is undefined.

[SaOgaz]

@nmearl if that's truly the case, the check might be leftover from an earlier version of specutils, should I remove it?

[nmearl]

I'm inclined to say yes, you should remove it, because if self.wcs is None, then there are definite problems, hah.

[SaOgaz]

Test failure unrelated to this PR.