Add truncation of timeline label

[jCHENEBY]

Fix cBioPortal/cbioportal#10448. Add truncation to timeline labels. Also add padding between end of label and arrow.

Describe changes proposed in this pull request:

• Change type of balise for TrackHeader label that display Timeline let bar and modify css accordingly
• Add some padding to end of label
• Remove unused import

With added padding

Demo of tooltip. Notes, I could not find other example so I "forced" ellipse by limiting timeline left bar size.

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[alisman]

@jCHENEBY not sure i'm doing something wrong but in testing it seems like it doesn't ever truncate.
https://genie.cbioportal.org/patient?studyId=crc_public_genie_bpc&caseId=GENIE-DFCI-001292

[jCHENEBY]

I had some time to look at it and the issue was that the left bar increased width to fit the label instead of truncated. I have set a fix max width to solve the issue.

I do not have access to the Genie database, but it seemed to work for this patient: https://www.cbioportal.org/patient/genomicEvolution?studyId=brca_hta9_htan_2022&caseId=HTA9_1&genomicEvolutionSettings=%7B%22showTimeline%22%3A%22true%22%2C%22showOnlySelectedMutationsInTable%22%3A%22false%22%7D

I also noticed that when the font-size it set to 12px and lower, the tooltip was not displayed for the first truncated label only. I did a quick and dirty fix and set the font-size for the left-bar at 12.5px. Please let me know if you have a more elegant solution.