Mesh one MSRE graphite stringer

[anshchaube]

• [x] Square plane
• [x] Make channel cutaways
• [x] Point for pyramid tip - join to pyramid base
• [x] Extrude pyramid base only to get channel of appropriate length
• [ ] Find out how to reuse stringer in a repeating pattern - separate issue?

[anshchaube]

Note: current stringer base model needs further domain decomposition in the top right quadrant.

[anshchaube]

• [ ] Ask @dshaver-ANL how to create pyramid-like tip of stringer using Nek's mesh deformation capabilities.

[anshchaube]

( 20/7/19: Kirk recommends using a CAD software.)

Currently trying to mesh the tip separately in issue #14 as meshing the tip and the fluid conformally is a non-trivial task.