Add login button to every page

[pedronunes19]

Closes #231

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 :tada:

Comparison is base (e2c6463) 89.05% compared to head (e0667df) 89.07%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #311 +/- ## =========================================== + Coverage 89.05% 89.07% +0.01% =========================================== Files 176 176 Lines 3390 3395 +5 Branches 851 855 +4 =========================================== + Hits 3019 3024 +5 Misses 371 371 ``` | [Impacted Files](https://codecov.io/gh/NIAEFEUP/nijobs-fe/pull/311?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NIAEFEUP) | Coverage Δ | | |---|---|---| | [src/components/Navbar/Auth/LoginForm.js](https://codecov.io/gh/NIAEFEUP/nijobs-fe/pull/311?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NIAEFEUP#diff-c3JjL2NvbXBvbmVudHMvTmF2YmFyL0F1dGgvTG9naW5Gb3JtLmpz) | `100.00% <100.00%> (ø)` | | | [src/components/Navbar/index.js](https://codecov.io/gh/NIAEFEUP/nijobs-fe/pull/311?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NIAEFEUP#diff-c3JjL2NvbXBvbmVudHMvTmF2YmFyL2luZGV4Lmpz) | `92.50% <100.00%> (+0.83%)` | :arrow_up: |

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[pedronunes19]

Login Icon (Material UI 5): https://mui.com/material-ui/material-icons/?selected=Login ExitToApp (Material UI 4): https://v4.mui.com/pt/components/material-icons/

The later was used since we're using version 4.

[Naapperas]

Just checked the preview, I think the text looks a bit small @pedronunes19