Align screen output and clean up code a bit

These are just some cosmetic changes to the code in `output_pimd.c` and a change of the screen output from PIMD such that it is aligned a better structures.

Old output looks like this:

    ********************************************************
    QUANTITY          =  INSTANTANEOUS    AVERAGE           
    --------------------------------------------------------
    Ensemble          = NVT     
    Time step         = 10
    ----------------- 
    Econv             = 0.0001402389757 4.89907966e-05
    Energy            = 0.2693688062 0.3024322688
    Total PE          = -0.7989847022 -0.7374200883
    Intermol PE       = -1.224513323 -1.249663783
    Intramol PE       = 0.4255286204 0.5122436943
    Fict. Atm KE      = 0.2670883771 0.2599630893
    Prim KE           = 0.5017316799 0.5376492696
    Vir KE            = 0.3872636727 0.4743091577
    ----------------- 
    Atm Deg. Free     = 384
    Fict. Atm Temperature   = 319.4710851 310.9483502 
    NHC Temperature   = 297.5718032 299.075515
    Bead NHC Temperature   = 311.7561253 312.7250993
    ----------------- 
    Pressure          = -809.6297108 -3485.526518
    Inter Pressure    = 30265.00168 29813.07322
    Intra Pressure    = -34039.32721 -36057.89984
    Kinetic Pressure  = 2769.918675 2769.918675
    Avg  P11,P22,P33  = 977.0421833 -7549.517078 -3884.104661 
    Inst P11,P22,P33  = -2190.306944 7344.824391 -7583.406579 
    Avg  P12,P13,P23  = -180.0040701 1859.004343 853.3578499 
    Inst P12,P13,P23  = -947.3619836 -221.1696057 -4513.845127 
    Avg  P21,P31,P32  = -116.7630508 1714.205037 959.4050595 
    Inst P21,P31,P32  = 395.7097972 -1020.999628 -4321.332496 
    ----------------- 
    Volume            = 1914.014007 1914.014007
    Inst cell lths    = 23.46284891 23.46284891 23.46284891
    Avg  cell lths    = 23.46284891 23.46284891 23.46284891
    Inst cell angs    = 90 90 90
    Avg  cell angs    = 90 90 90
    ----------------- 
    Cpu time          = 0.05 0.049
    --------------------------------------------------------

    ********************************************************

New output looks like this:

    ****************************************************************************

    Ensemble          = NVT
    Time step         = 10
    Time              = 0.005 ps

    QUANTITY                 INSTANTANEOUS            AVERAGE
    ---------------------------------------------------------

    Econv             =       0.0005595523       0.0006326957
    Energy            =       1.6983019579       1.8030659200
    Total PE          =      -0.1345995051       0.2741859070
    Intermol PE       =      -1.3778722872      -1.3751872543
    Intramol PE       =       1.2432727821       1.6493731613
    Fict. Atm KE      =       0.4582253658       0.3822200033
    Prim KE           =       0.0175579007      -0.0546814396
    Vir KE            =       0.6786092287       1.1627372446

    Fict. Atm Temp.   =     548.0948156092     457.1829013887
    NHC Temperature   =     306.6050657649     302.8290258844
    Bead NHC Temp.    =     330.5708451618     319.1237026828

    Pressure          =  -42641.5318136551  -20526.1331679271
    Inter Pressure    =   29216.7231523526   29032.6073377060
    Intra Pressure    =  -77145.8499280480  -54074.8762384020
    Kinetic Pressure  =    2769.9186752095    2769.9186752095
    Volume            =    1914.0140072960    1914.0140072960

    Cpu time          =       0.0500000000       0.0490000000

    QUANTITY
    ----------------------------------------------------------------------------

    Avg  P11,P22,P33  =  -14910.4143875558  -23205.7085195575  -23462.2765966679
    Inst P11,P22,P33  =  -49844.3217884253  -29985.4181650854  -48094.8554874546
    Avg  P12,P13,P23  =   -1176.5610654266    4004.3437479120    2408.2049813776
    Inst P12,P13,P23  =    -596.7977042046    4221.9970231885    3038.2835946803
    Avg  P21,P31,P32  =   -2329.9029635704    5195.1797709332    2320.9234187626
    Inst P21,P31,P32  =    1311.9423045843    3518.8656554426    2983.8595194015

    Inst cell lths    =      23.4628489144      23.4628489144      23.4628489144
    Avg  cell lths    =      23.4628489144      23.4628489144      23.4628489144
    Inst cell angs    =      90.0000000000      90.0000000000      90.0000000000
    Avg  cell angs    =      90.0000000000      90.0000000000      90.0000000000

    ****************************************************************************