Adds plotConsProfiles function

[TomSmithCGAT]

This PR adds a function, plotConsProfiles, to plot the consensus profile outputted from mrkConsProfiles. See #130 for motivation.

I've been through Hadley Wickham's R Packages online materials to try and ensure I've updated and checked everything correctly. I've added documentation and a short example to the "pRoloc-tutorial" vignette where it seemed appropriate. devtools::check() currently returns the following warnings/notes which don't appear to relate to the changes herein.

── R CMD check results ────────────────────────────────────────────────────────────────────────────────────────────────── pRoloc 1.23.1 ────
Duration: 14m 40s

❯ checking compiled code ... OK
   WARNING
  ‘qpdf’ is needed for checks on size reduction of PDFs

❯ checking installed package size ... NOTE
    installed size is 15.7Mb
    sub-directories of 1Mb or more:
      R     1.1Mb
      doc  12.9Mb

❯ checking dependencies in R code ... NOTE
  Unexported objects imported by ':::' calls:
    ‘MLInterfaces:::.macroF1’ ‘MLInterfaces:::.precision’
    ‘MLInterfaces:::.recall’ ‘MLInterfaces:::es2df’
    ‘MSnbase:::.sameNbCol’ ‘MSnbase:::getVariableName’
    ‘MSnbase:::logging’ ‘MSnbase:::nologging’ ‘caret:::predict.plsda’
    See the note in ?`:::` about the use of this operator.
  There are ::: calls to the package's namespace in its code. A package
    almost never needs to use ::: for its own objects:
    ‘.ComponentParam’ ‘.MCMCChain’ ‘.MCMCChains’ ‘.MCMCParams’
    ‘.MCMCSummary’ ‘chains’

❯ checking R code for possible problems ... NOTE
  Found the following possibly unsafe calls:
  File ‘pRoloc/R/annotation.R’:
    unlockBinding("params", .pRolocEnv)

  plotConsProfiles: no visible binding for global variable ‘feature’
  Undefined global functions or variables:
    feature

0 errors ✔ | 1 warning ✖ | 3 notes ✖

[codecov-io]

Codecov Report

Merging #131 into master will decrease coverage by 0.17%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #131      +/-   ##
==========================================
- Coverage   41.93%   41.75%   -0.18%     
==========================================
  Files          50       50              
  Lines        5583     5607      +24     
==========================================
  Hits         2341     2341              
- Misses       3242     3266      +24

Impacted Files	Coverage Δ
R/plotting.R	32% <0%> (-1.91%)	:arrow_down:

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[lgatto]

You can ignore the other points raised during package checking.