Add new column label bars to heatmap

[bhavyaac]

(Based on discussions from issue #21 that has been closed.)

Currently, the heat map includes a coloured bar above the main plot to categorize cluster columns into general cell types. It would also be useful to have bars giving information on the brain region (forebrain vs. pons) as well as time point of the cluster. I can include toggles to turn each bar on/off, so that the user can focus on the information that they are interested in.

[bhavyaac]

Just added this feature:

There are checkboxes in the sidebar to select which annotation(s) to display.

Known issues that I still must fix:

• [x] The colour palette specification for the annotation(s) does not work anymore, R is using a default palette
• [x] For some reason, P6 samples are not being labelled as such, although other time points seem to be fine...?
• [x] The colour palette legends on the side are cut off at the bottom because they take up much more space than the heatmap height
• [x] Unselecting all of the annotation choices gives an error - I should either use validate() to prevent the user from doing this, or I should include functionality for creating the Pheatmap without annotations

[bhavyaac]

Update: I've fixed the heatmap dimensions to show full legend and also implemented validate() telling the user to enter at least one column annotation.

There is something seriously wrong with the grepl() command on the Sample column (output of bubble_prep()) that I have been using, given that I just got the following incorrectly-annotated heatmap during testing: Not all of these samples are P6, and all of them are clearly either Forebrain or Pons. I need to fix that grep command, not sure how to debug it easily though! Edit: alternatively, it might be an issue with the contents/presence of the Sample column, so I can switch to doing a grep on the cluster name itself